Improve contributor documentation

Author: david-christiansen

CONTRIBUTING.md

@@ -9,8 +9,9 @@ The message index is in the directory `message-index`.
 
 ## Building GHC with Error Codes
 
-Please follow the instructions on [building GHC with Hadrian](https://gitlab.haskell.org/ghc/ghc/-/wikis/building/hadrian), using a version of the `master` branch from after 13 September, 2022 or a release of version 9.6.1 or higher.
-Your error messages would then contain an ID.
+Until the release of GHC 9.6.1, error and warning IDs are only available using a development version of GHC. Please
+follow the instructions on [building GHC with Hadrian](https://gitlab.haskell.org/ghc/ghc/-/wikis/building/hadrian),
+using a version of the `master` branch from after 13 September, 2022. Your error messages would then contain an ID:
 
 ```
 $ _build/stage1/bin/ghc --interactive

README.md

@@ -1,7 +1,7 @@
 # The Haskell Message Index
 [![.github/workflows/deploy.yml](https://github.com/haskellfoundation/error-message-index/actions/workflows/deploy.yml/badge.svg?branch=main)](https://github.com/haskellfoundation/error-message-index/actions/workflows/deploy.yml)
 
-Haskell tooling emits a variety of errors, warnings, and other messages. In an unreleased branch, GHC emits a unique code for each message that allows it to be identified. This site allows these codes to be looked up, providing examples, context, and further information that can make them easier to understand.
+Haskell tooling emits a variety of errors, warnings, and other messages. In the latest development versions that are leading to the release of version 9.6.1, GHC emits a unique code for each message that allows it to be identified. This site allows these codes to be looked up, providing examples, context, and further information that can make them easier to understand.
 
 Please see [CONTRIBUTING.md](./CONTRIBUTING.md) for instructions on improving the site. Thanks!
 

tech-choices.md

@@ -2,5 +2,13 @@
 
 The website generated by `message-index` uses a few JS components.
 
-- [highlight.js](https://highlightjs.org/) for highlighting blocks of code. [License: BSD 3-Clause](https://github.com/highlightjs/highlight.js/blob/main/LICENSE).
-- [TableFilter](http://www.tablefilter.com/) for the filtering functionality in the error message table. [License: MIT](https://github.com/koalyptus/TableFilter/blob/master/LICENSE).
+ - [highlight.js](https://highlightjs.org/) for highlighting blocks of code. [License: BSD 3-Clause](https://github.com/highlightjs/highlight.js/blob/main/LICENSE).
+ - [TableFilter](http://www.tablefilter.com/) for the filtering functionality in the error message table. [License: MIT](https://github.com/koalyptus/TableFilter/blob/master/LICENSE).
+
+Generally speaking, we choose technology for this site based on the following criteria:
+
+ * The build process for the site should be simple, relying on no build tools or package managers aside from `cabal` or `stack`
+ * CSS and Javascript code should be straightforward to maintain by someone who has only rudimentary front-end development skills
+ * The generated site should consist only of static files that can be hosted anywhere
+ * URLs should be predictable, and easy for external tools to generate (e.g. so IDEs can link to error documentation)
+