Fix PowerShell command (#1202)

Quoting PowerShell: The term 'python.bat' is not recognized as the name
of a cmdlet, function, script file, or operable program.

.\python.bat however works perfectly.

getting-started/pull-request-lifecycle.rst

@@ -249,7 +249,7 @@ On *Windows* (after any successful build):
 
 .. code-block:: dosbatch
 
-   python.bat Tools\patchcheck\patchcheck.py
+   .\python.bat Tools\patchcheck\patchcheck.py
 
 The automated patch checklist runs through: