Update Maintainers and Contributors file for overassigning issues (#481)

* Updated the contributing file

* Updated the contributing file

Author: TimOsahenru

CONTRIBUTING.md

@@ -38,6 +38,7 @@ Follow these steps and note these guidelines to begin contributing:
 
 ## Working on an issue
 
+- Please create a separate branch for each issue you work on. Avoid working on multiple issues from the same branch, as this can complicate the review process
 - The easiest way to make changes and and test them is by using [![GitHub Codespaces](https://github.com/codespaces/badge.svg)](https://codespaces.new/BlackPythonDevs/blackpythondevs.github.io)
 
 - You can also access the Codespaces from the repository main page: