docs(marketplace): use "vsce package" image URLs #3270

Everything is fine (>'')>

BACKGROUND:
`vsce package` always replaces *relative local* image paths with URLs:
https://github.com/microsoft/vscode-vsce/blob/9478dbd11ea2e7adb23ec72923e889c7bb215263/src/package.ts#L885
For example,
    ![creds](./resources/marketplace/vscode/creds.gif)
is replaced with:
    ![creds](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/resources/marketplace/vscode/creds.gif)

PROBLEM:
In the parent commit, before merging the PR, when I checked the URL:
    https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/creds.gif
I wrongly thought the URL was "broken" (didn't know that `raw/HEAD/` was
valid GitHub URL "syntax"). But after merging to mainline, the URL
actually works and redirects to:
    https://raw.githubusercontent.com/aws/aws-toolkit-vscode/04baf36689134e48a4db4ffb1d97b16584388141/docs/marketplace/vscode/creds.gif

SOLUTION:
- Update the URLs to use the same format that would be forced by `vsce`:
  https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/…
    - This is more explicit and hopefully less confusing for other contributors.
- Add a note in CONTRIBUTING.md

Author: justinmk3

CONTRIBUTING.md

@@ -341,6 +341,20 @@ As a simple example, let's say I wanted to add a new icon for CloudWatch log str
 
 The Toolkit codebase contains logic in `src/dev/beta.ts` to support development during private betas. Creating a beta artifact requires a _stable_ URL to source Toolkit builds from. This URL should be added to `src/dev/config.ts`. Subsequent Toolkit artifacts will have their version set to `1.999.0` with a commit hash. Builds will automatically query the URL to check for a new build once a day and on every reload.
 
+### VSCode Marketplace
+
+The [marketplace page](https://marketplace.visualstudio.com/itemdetails?itemName=AmazonWebServices.aws-toolkit-vscode)
+is defined in `README.quickstart.vscode.md` (which replaces `README.md` during
+the release automation). The `vsce` package tool always [replaces relative image paths](https://github.com/microsoft/vscode-vsce/blob/9478dbd11ea2e7adb23ec72923e889c7bb215263/src/package.ts#L885)
+with URLs pointing to `HEAD` on GitHub (`https://github.com/aws/aws-toolkit-vscode/raw/HEAD/…/foo.gif`).
+
+Note therefore:
+
+1. Don't delete images from `docs/marketplace/` unless the _current published_
+   AWS Toolkit release doesn't depend on them.
+2. `HEAD` implies that the URL depends on the current _default branch_ (i.e.
+   `master`). Changes to other branches won't affect the marketplace page.
+
 ## Importing icons from other open source repos
 
 If you are contribuing visual assets from other open source repos, the source repo must have a compatible license (such as MIT), and we need to document the source of the images. Follow these steps:

README.quickstart.vscode.md

@@ -14,57 +14,57 @@ The AWS Toolkit lets you interact with AWS directly from VS Code. Ready to insta
 
 Access AWS resources across your accounts and regions.
 
-![creds](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/creds.gif)
+![creds](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/creds.gif)
 
 ### S3 support
 
 View, create, and edit S3 buckets, folders, and files.
 
-![S3](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/S3.gif)
+![S3](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/S3.gif)
 
 ### Download & upload Lambda functions
 
-![download-Lambda](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/download-Lambda.gif)
+![download-Lambda](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/download-Lambda.gif)
 
 ## Troubleshoot AWS from the IDE
 
 ### Lambda
 
 Step-through AWS Lambda functions using the VS Code debugger
 
-![Lambda_step_through_debugging](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/Lambda_step_through_debugging.gif)
+![Lambda_step_through_debugging](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/Lambda_step_through_debugging.gif)
 
 ### CloudWatch Logs
 
 Find logs generated by your AWS resources
 
-![cw_logs](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/cw_logs.gif)
+![cw_logs](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/cw_logs.gif)
 
 ### ECS
 
 Execute commands against running ECS containers (or open a terminal)
 
-![ecs-terminal](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/ecs-terminal.gif)
+![ecs-terminal](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/ecs-terminal.gif)
 
 ## Write and edit code faster
 
 ### [Amazon CodeWhisperer](https://aws.amazon.com/codewhisperer/)
 
 Build applications faster with automatic code recommendations based on the code and comments in VS Code.
 
-![CodeWhisperer](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/codewhisperer.gif)
+![CodeWhisperer](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/codewhisperer.gif)
 
 ### [Amazon CodeCatalyst](https://aws.amazon.com/codecatalyst/)
 
 Launch VS Code in a cloud development environment, powered by Amazon CodeCatalyst.
 
-![CodeCatalyst](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/CC_dev_env.gif)
+![CodeCatalyst](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/CC_dev_env.gif)
 
 ### CloudFormation
 
 Autocompletion and syntax support for CloudFormation templates
 
-![cfn_autocompletion](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/cfn_autocompletion.gif)
+![cfn_autocompletion](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/cfn_autocompletion.gif)
 
 ## More features
 
@@ -88,7 +88,7 @@ For a full list of features, visit [our documentation](https://docs.aws.amazon.c
     2. **CodeWhisperer** - connect using an AWS Builder ID or IAM Identity Center (formerly SSO)
     3. **CodeCatalyst** - connect using AWS Builder ID
 
-![getting-started](https://raw.githubusercontent.com/aws/aws-toolkit-vscode/master/docs/marketplace/vscode/getting-started.gif)
+![getting-started](https://github.com/aws/aws-toolkit-vscode/raw/HEAD/docs/marketplace/vscode/getting-started.gif)
 
 ## Troubleshooting