Add documentation how to build installers (#21683)

* Add documentation how to build installers
Also add small index for the Docs folder

* Fix PR comments

* Update casing for the command line parameter

* Remove duplicate section

docs/BuildFromSource.md

@@ -230,6 +230,16 @@ TargetOsName             | The base runtime identifier to build for (win, linux,
 After building ASP.NET Core from source, you will need to install and use your local version of ASP.NET Core.
 See ["Artifacts"](./Artifacts.md) for more explanation of the different folders produced by a build.
 
+Building installers does not run as part of `build.cmd` run without parameters, so you should opt-in for building them: 
+
+```ps1
+.\build.cmd -all -pack -arch x64
+.\build.cmd -all -pack -arch x86 -noBuildJava
+.\build.cmd -buildInstallers
+```
+
+*Note*: Additional build steps listed above aren't necessary on Linux or macOS.
+
 * Run the installers produced in `artifacts/installers/{Debug, Release}/` for your platform.
 * Add a NuGet.Config to your project directory with the following content:
 

docs/README.md

@@ -3,3 +3,9 @@ Contributor documentation
 
 The primary audience for documentation in this folder is contributors to ASP.NET Core.
 If you are looking for documentation on how to *use* ASP.NET Core, go to <https://docs.asp.net>.
+
+# ASP.NET Core developer workflow
+
+- [Building from source](BuildFromSource.md)
+- [Troubleshooting build errors](BuildErrors.md)
+- [Artifacts structure](Artifacts.md)