[docs] Add Python coding standard to documentation

As discussed on the forums:

https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style/

Reviewed By: jhenderson, JDevlieghere

Differential Revision: https://reviews.llvm.org/D143852

Author: tru

llvm/docs/CodingStandards.rst

@@ -50,6 +50,9 @@ code imported into the tree. Generally, our preference is for standards
 conforming, modern, and portable C++ code as the implementation language of
 choice.
 
+For automation, build-systems and utility scripts Python is preferred and
+is widely used in the LLVM repository already.
+
 C++ Standard Versions
 ---------------------
 
@@ -102,6 +105,21 @@ For more information about LLVM's data structures and the tradeoffs they make,
 please consult `that section of the programmer's manual
 <https://llvm.org/docs/ProgrammersManual.html#picking-the-right-data-structure-for-a-task>`_.
 
+Python version and Source Code Formatting
+-----------------------------------------
+
+The current minimum version of Python required is documented in the :doc:`GettingStarted`
+section. Python code in the LLVM repository should only use language features
+available in this version of Python.
+
+The Python code within the LLVM repository should adhere to the formatting guidelines
+outlined in `PEP-8 <https://peps.python.org/pep-0008/>`_.
+
+For consistency and to limit churn, code should be automatically formatted with the
+`black <https://github.com/psf/black>`_ utility. Black allows changing the formatting
+rules based on major version. In order to avoid unecessary churn in the formatting rules
+we currently use black version 23.x in LLVM.
+
 Mechanical Source Issues
 ========================