Backend team assignment - Contributing.md file

Title

Adds a contributing file to our project, team assignment for backend team for week 13

If this fixes a bug or resolves an issue, provide a link to that issue. Give a detailed description that answers:

what is the purpose of this PR? Introduces a contributing file to our project
what is the original vs the new behaviour? NA
what bug does this PR attempt to fix? NA
what is documented in the new documentation? How to contribute to our project.

Put an x in the boxes that apply

[ ] Feature (non-breaking change which adds functionality)
[ ] Bug Fix (non-breaking change that fixes an issue)
[ ] Breaking Change (feature/fix that causes existing features to not work as expected)
[x] Documentation

[x] I have read the [contribute]contributing doc
[ ] Classes, scripts, and environment variables follow existing naming convention
[ ] Lint and Unit tests pass locally
[ ] New features on hardware have been tested on a local Raspberry Pi
[ ] Mention new programs/binaries if any must be installed along with this change
[ ] Mention new environment variables if any have been added to hardware/env file
[x] Test coverage should not drop more than 3%
[ ] Any new required python modules are added to the requirements.txt