docs: Update instruction for docfx

Author: linkdotnet

docs/README.md

@@ -21,16 +21,17 @@ These sample components, source files, and tests source files are included in th
 The following chapter describes how you can run and view the documentation locally
 
 ### Requirements
-You will need the following tool installed:
+The following tools are required to build and view the documentation locally:
 * The [`dotnet serve` tool](https://github.com/natemcmaster/dotnet-serve)
+* The `docfx` dotnet global tool: `dotnet tool install -g docfx`.
 * [DocFx](https://dotnet.github.io/docfx/tutorial/docfx_getting_started).
 
 ### View the documentation
 
-1. Build the `bunit.sln` solution in the root folder.
-2. From `docs/site` run `dotnet build`. If you get warnings from running `dotnet build`, try running it again.
-3. Inside `docs/site` run `dotnet run` to start the generation.
-4. From `docs/` run `serve-docs.cmd`. This will start up a local web server, hosting the generated documentation site.
+1. Build the `bunit.sln` solution in the root folder in release configuration `dotnet build -c Release`.
+2. From `docs/site` run `docfx metadata` to generate the documentation site's metadata.
+3. After that run `docfx build` to generate the documentation site.
+4. From `docs/` run `serve-docs.cmd`. This will start up a local web server (using `dotnet serve`), hosting the generated documentation site.
 5. After changing samples from `docs/samples`, run `dotnet test`. This will compile the sample components and run the sample tests.
 
 ## Documentation Writing Rules