Add instructions for cloning and debugging (#5276)

Add some instructions for getting the latest source code from the master branch.
Also add a link to some instructions for how to debug the compiler.

DEVGUIDE.md

 # Development Guide
 
+## Get the Latest F# Compiler Source Code
+
+Get the latest source code from the master branch by running this git command:
+
+    git clone https://github.com/Microsoft/visualfsharp.git
+    
+Before running the build scripts, ensure that you have cleaned up the visualfsharp repo by running this git command:
+
+    git clean -xfd
+
+This will remove any files that are not under version control. This is necessary only if you have already attempted to build the solution or have made other changes that might prevent it from building.
+
+## Installing Dependencies and Building
+
 Follow the instructions below to build and develop the F# Compiler, Core Library and tools on Windows, macOS and Linux.
 
 - [Developing the F# Compiler (Windows)](#developing-the-f-compiler-windows)
@@ -20,10 +34,6 @@ Install
 
 2. The command prompt must have Administrator rights (`Run as Administrator`).
 
-Before running the build scripts, ensure that you have cleaned up the visualfsharp repo by running this git command:
-
-    git clean -xfd
-
 On Windows you can build the F# compiler for .NET Framework as follows:
 
     build.cmd
@@ -195,7 +205,11 @@ For **Release**:
 
     vsintegration\update-vsintegration.cmd release
 
-# Notes
+## Debugging the F# Compiler
+
+See the "Debugging The Compiler" section of this [article](https://medium.com/@willie.tetlow/f-mentorship-week-1-36f51d3812d4)
+
+## Notes
 
 #### Windows: Links to  Additional frameworks