add contribution guidance (#46)

* add contribution guidance

* update contribution guidance, add git issue template

CONTRIBUTING.md

@@ -0,0 +1,25 @@
+# Contributing
+When contributing to this repository, please first discuss the change you wish
+to make, added functionality you'd like to see, or bug you've found via one
+of the following:
+- Raising a github issue using the issue template;
+- Emailing [email protected];
+- Contacting the py-af-colours team on the data-vis govdatascience channel;
+- Using the Accessibility and Presentation/Dissemination of Statistics Basecamp groups.
+
+## Pull/merge request process
+1. Branch from the `main` branch. If you are implementing a feature name it
+`feature/name_of_feature`, if you are implementing a bugfix name it
+`bug/issue_name`.
+2. Update the README.md and other documentation with details of major changes
+to the interface, this includes new environment variables, useful file
+locations and container parameters. If you have added new functionality,
+please include an example.
+3. Once you are ready for review please open a pull/merge request to the
+`main` branch.
+4. You may merge the Pull/Merge Request in once you have the sign-off of an owner.
+
+## Code style
+- We follow the [PEP8](https://peps.python.org/pep-0008/) style.
+- We use the [numpydoc](https://numpydoc.readthedocs.io/en/latest/format.html)
+format for documenting features using docstrings.

ISSUE_TEMPLATE.md

@@ -0,0 +1,13 @@
+# Issue Template
+title: <Short title>
+author: <Full name>
+
+# Issue
+<Brief explanation of problem>
+
+# Proposed Change
+<If proposing new functionality; any ideas, suggestions, options, including links to guidance if relevant>
+
+# Type of Change Requested
+[ ] Bug fix
+[ ] New feature