Add conditional text to the README and update the RIDs

Author: jeffkl

src/ProjectTemplates/Microsoft.Extensions.AI.Templates/src/McpServer/McpServer-CSharp/.template.config/template.json

@@ -86,5 +86,23 @@
       },
       "continueOnError": true
     }
-  ]
+  ],
+  "SpecialCustomOperations": {
+    "**/*.md": {
+      "operations": [
+        {
+          "type": "conditional",
+          "configuration": {
+            "if": [ "#### ---#if" ],
+            "else": [ "#### ---#else" ],
+            "elseif": [ "#### ---#elseif", "#### ---#elif" ],
+            "endif": [ "#### ---#endif" ],
+            "trim": "true",
+            "wholeLine": "true",
+            "evaluator": "C++"
+          }
+        }
+      ]
+    }
+  }
 }

src/ProjectTemplates/Microsoft.Extensions.AI.Templates/src/McpServer/McpServer-CSharp/McpServer-CSharp.csproj.in

@@ -4,7 +4,7 @@
     <TargetFramework Condition="'$(TargetFrameworkOverride)' == ''">net9.0</TargetFramework>
     <TargetFramework Condition="'$(TargetFrameworkOverride)' != ''">TargetFrameworkOverride</TargetFramework>
     <!--#if (SelfContained || NativeAot)-->
-    <RuntimeIdentifiers>win-x64;win-arm64;osx-arm64;linux-x64;linux-arm64</RuntimeIdentifiers>
+    <RuntimeIdentifiers>win-x64;win-arm64;osx-arm64;linux-x64;linux-arm64;linux-musl-x64</RuntimeIdentifiers>
     <!--#else-->
     <RollForward>Major</RollForward>
     <!--#endif -->

src/ProjectTemplates/Microsoft.Extensions.AI.Templates/src/McpServer/McpServer-CSharp/README.md

@@ -1,6 +1,26 @@
 # MCP Server
 
-This README was created using the C# MCP server project template. It demonstrates how you can easily create an MCP server using C# and publish it as a NuGet package.
+This README was created using the C# MCP server project template.
+It demonstrates how you can easily create an MCP server using C# and publish it as a NuGet package.
+
+#### ---#if (SelfContained)
+The MCP server is built as a self-contained application and does not require the .NET runtime to be installed on the target machine.
+However, since it is self-contained, it must be built for each target platform separately.
+By default, the template is configured to build for:
+* `win-x64`
+* `win-arm64`
+* `osx-arm64`
+* `linux-x64`
+* `linux-arm64`
+* `linux-musl-x64`
+
+If your users have require more platforms to be supported, update the list of runtime identifiers in the project's `<RuntimeIdentifers />` element.
+#### ---#else
+The MCP server is built as a framework-dependent application and requires the .NET runtime to be installed on the target machine.
+The application is configured to roll-forward to the next highest major version of the runtime if one is available on the target machine.
+If an applicable .NET runtime is not available, the MCP server will not start.
+Consider building the MCP server as a self-contained application if you want to avoid this dependency.
+#### ---#endif
 
 See [aka.ms/nuget/mcp/guide](https://aka.ms/nuget/mcp/guide) for the full guide.