Fix two typos in documentation for tool prerequisites

Correct path for script to activate a python virtual environment.

Code snippet showing how to install the python requirements for a repository is referencing the file as it was originally named (requirements.txt).  Now in most Project Mu and Edk2 repos the file is named pip-requirements.txt. Update sample to reflect that.

docs/CodeDevelopment/prerequisites.md

@@ -145,14 +145,14 @@ Do this each time you open a new command window to build your workspace.
 2. run activate script - for windows cmd prompt (cmd.exe) do this
 
     ``` cmd
-    <your virtual env name>\Script\activate
+    <your virtual env name>\Scripts\activate
     ```
 
 3. cd into your workspace directory
 4. Update/Install your python pip requirements.  This is generally at the workspace root.
 
     ``` cmd
-    pip install --upgrade -r requirements.txt
+    pip install --upgrade -r pip-requirements.txt
     ```
 
 5. Do dev work and run your builds!