Update ProjectTemplates README.md (#27969)

Author: HaoK

src/ProjectTemplates/README.md

@@ -1,23 +1,45 @@
 # Templates
 
-## Getting Started
 These are project templates which are used in .NET Core for creating ASP.NET Core applications.
 
-## Prerequisites
+## Description
+
+The following contains a description of each sub-directory in the `ProjectTemplates` directory.
+
+- `BlazorTemplates.Tests`: Contains the source files for the Blazor template tests, these are currently split out due to not being Helix ready yet.
+- `Shared`: Contains a collection of shared constants and helper methods/classes including the infrastructure for managing dotnet processes to create, build, run template tests.
+- `Web.Client.ItemTemplates`: Contains the Web Client-Side File templates, includes things like less, scss, and typescript
+- `Web.ItemTemplates`: Contains the Web File templates, includes things like: protobuf, razor component, razor page, view import and start pages
+- `Web.ProjectTemplates`: Contains the ASP.NET Core Web Template pack, including Blazor Server, WASM, Empty, Grpc, Razor Class Library, RazorPages, MVC, WebApi.
+- `Web.Spa.ProjectTemplates`: Contains the Single Page Application templates for ASP.NET Core, including Anuglar, React, ReactRedux.
+- `migrations`: Contains migration related scripts.
+- `scripts`: Contains a collection of scripts that help running tests locally that avoid having to install the templates to the machine.
+- `test`: Contains the end to end template tests.
+- `testassets`: Contains assets used by the tests, like a dotnet tools installer
+
+### Build
+
 Some projects in this repository (like SignalR Java Client) require JDK installation and configuration of `JAVA_HOME` environment variable.
 1. If you don't have the JDK installed, you can find it from https://www.oracle.com/technetwork/java/javase/downloads/index.html
 1. After installation define a new environment variable named `JAVA_HOME` pointing to the root of the latest JDK installation (for Windows it will be something like `c:\Program Files\Java\jdk-12`).
 1. Add the `%JAVA_HOME%\bin` directory to the `PATH` environment variable
 
-## Building Templates
-1. Run `. .\activate.ps1` if you haven't already.
+To build the ProjectTemplates:
 
-1. Run `git submodule update --init --recursive` if you haven't already.
-1. Run `git submodule update` to update submodules.
 1. Run `build.cmd -all -pack -configuration Release` in the repository root to build all of the dependencies.
-1. Run `build.cmd -pack -NoRestore -NoBuilddeps -configuration Release` in this directory will produce NuGet packages for each class of template in the artifacts directory.
+1. Run `build.cmd -pack -NoRestore -NoBuilddeps -configuration Release` in src/ProjectTemplates directory to produce NuGet packages for each class of template in the artifacts directory.
+
+### Test
+
+To run the ProjectTemplate tests:
+
 1. Because the templates build against the version of `Microsoft.AspNetCore.App` that was built during the previous step, it is NOT advised that you install templates created on your local machine via `dotnet new -i [nupkgPath]`. Instead, use the `Run-[Template]-Locally.ps1` scripts in the script folder. These scripts do `dotnet new -i` with your packages, but also apply a series of fixes and tweaks to the created template which keep the fact that you don't have a production `Microsoft.AspNetCore.App` from interfering.
 1. The ASP.NET localhost development certificate must also be installed and trusted or else you'll get a test error "Certificate error: Navigation blocked".
 1. Run `.\build.cmd -test -NoRestore -NoBuild -NoBuilddeps -configuration Release "/p:RunTemplateTests=true"` to run template tests.
 
-** Note** Templating tests require Visual Studio unless a full build (CI) is performed.
+** Note** ProjectTemplates tests require Visual Studio unless a full build (CI) is performed.
+
+## More Information
+
+For more information, see the [ASP.NET Core README](../../README.md).
+