Update Git setup documentation

Now that everyone needs all the submodules. Much simpler.

docs/building/windows-core.md

@@ -47,17 +47,9 @@ Git Setup
 ---------
 
 Using Git requires it to be setup correctly; refer to the
+[README](../../README.md) and
 [Contributing Guidelines](../../CONTRIBUTING.md).
 
-Please clone the superproject (this repo) and initialize a subset of
-the submodules:
-
-```sh
-git clone https://github.com/PowerShell/PowerShell.git
-cd PowerShell
-git submodule update --init -- src/windows-build src/Modules/Pester
-```
-
 Build using our module
 ======================