Add doc for ReadmeUriTemplate (#3382)

* add new resource doc

* Updated the implementation guide

* remove extra line

* Update URL placeholders to required

Author: jgonz120

docs/TOC.md

@@ -128,6 +128,7 @@
 #### [Package metadata](api/registration-base-url-resource.md)
 #### [Push and delete](api/package-publish-resource.md)
 #### [Push symbol packages](api/symbol-package-publish-resource.md)
+#### [README URI](api/readme-template-resource.md)
 #### [Report abuse URL](api/report-abuse-resource.md)
 #### [Repository signatures](api/repository-signatures-resource.md)
 #### [Search](api/search-query-service-resource.md)

docs/api/implementation-guide.md

@@ -35,6 +35,7 @@ To assist authors of existing NuGet repositories keep up to date with NuGet's ne
 ||Added `packageTypes` query parameter to `SearchQueryService` requests|
 |2021|[Embedded readme](#embedded-files)|
 |2023|[PreAuthenticate authenticated requests](#url-structure-for-authenticated-feeds) <br/> [`VulnerabilityInfo` resource](#known-vulnerabilities-database-vulnerabilityinfo)|
+|2025|[Enable embedded README downloads](#enable-embedded-readme-downloads)|
 
 ## Owner field
 
@@ -140,3 +141,7 @@ In this case, every request to the service index will have additional latency, d
 
 While NuGet's V3 API was designed to work on a static file server, the search resource is the exception that always requires a dynamic web service to process requests.
 If you wish to host search, or indeed any other NuGet API resource, on different servers, in order to benefit from `HttpClientHandler`'s `PreAuthenticate`, you will need to use a reverse proxy to ensure all customer facing URLs in the service index meet the "same or subdirectory" rule.
+
+## Enable embedded README downloads
+
+A [new resource](./readme-template-resource.md) was documented for constructing a URL that can be used to download a README for a given package. This will allow client, like the Package Management UI in VS, to display the embedded README for packages which haven't been previously installed by the user. The client will construct this URL and attempt to download the README, using the response to the request to determine if a README is available. This means servers should expect multiple requests to the constructed endpoint as users navigate the PM UI. 

docs/api/overview.md

@@ -61,6 +61,7 @@ Resource name                                                        | Required
 [PackageBaseAddress](package-base-address-resource.md)               | yes      | Get package content (.nupkg).
 [PackageDetailsUriTemplate](package-details-template-resource.md)    | no       | Construct a URL to access a package details web page.
 [PackagePublish](package-publish-resource.md)                        | yes      | Push and delete (or unlist) packages.
+[ReadmeUriTemplate](readme-template-resource.md)                     | no       | Construct a URL to access a package's README.
 [RegistrationsBaseUrl](registration-base-url-resource.md)            | yes      | Get package metadata.
 [ReportAbuseUriTemplate](report-abuse-resource.md)                   | no       | Construct a URL to access a report abuse web page.
 [RepositorySignatures](repository-signatures-resource.md)            | no       | Get certificates used for repository signing.

docs/api/readme-template-resource.md

@@ -0,0 +1,62 @@
+---
+title: README Uri Template, NuGet API
+description: The README uri template allows clients to download the readme for a package, if available.
+author: jgonz120
+ms.author: jongonza
+ms.date: 1/6/2025
+ms.topic: reference
+ms.reviewer: 
+---
+
+# README Uri Template
+
+It is possible for a client to build a URL that can be used to download a README for a specific package.
+This will enable the clients to render the package's README without downloading the entire package.
+
+The resource used for building this URL is the `ReadmeUriTemplate` resource found in the
+[service index](service-index.md).
+
+## Versioning
+
+The following `@type` values are used:
+
+@type value                       | Notes
+--------------------------------- | -----
+ReadmeUriTemplate/6.13.0          | The initial release
+
+## URL template
+
+The URL for the following API is the value of the `@id` property associated with one of the aforementioned
+resource `@type` values.
+
+## HTTP methods
+
+The constructed URL must support the HTTP method `GET`
+
+## Construct the URL
+
+Given a known package ID and version, the client implementation can construct a URL to download the README. 
+
+The value of the `@id` is a URL string containing any of the following placeholder tokens:
+
+### URL placeholders
+
+Name        | Type    | Required | Notes
+----------- | ------- | -------- | -----
+`{lower_id}`      | string  | yes       | The package ID, lowercased
+`{lower_version}` | string  | yes       | The package version, lowercased
+
+Both `lower_id` and `lower_version` are lowercased using the rules implemented by .NET's
+[`System.String.ToLowerInvariant()`](/dotnet/api/system.string.tolowerinvariant?view=netstandard-2.0#System_String_ToLowerInvariant&preserve-view=true)
+method.
+
+The `lower_version` is the desired package version normalized using NuGet's version
+[normalization rules](../concepts/package-versioning.md#normalized-version-numbers). This means that build metadata
+that is allowed by the SemVer 2.0.0 specification must be excluded in this case.
+
+### Response body
+
+If the package has a readme, a 200 status code is returned. The response body will be the readme
+content itself.
+
+If the package does not have a readme, a 404 status code is returned.