Updating the CONTRIBUTING.md to include relevant links

CONTRIBUTING.md

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+# Assemblyline contributing guide
+
+This guide covers the basics of how to contribute to the Assemblyline project.
+
+Python code should follow the PEP8 guidelines defined here: [PEP8 Guidelines](https://www.python.org/dev/peps/pep-0008/).
+
+## Tell us want you want to build/fix
+Before you start coding anything you should connect with the Assemblyline community via the [Assemblyline Discord server](https://discord.gg/GUAy9wErNu) and/or the [central Assemblyline GitHub project](https://github.com/CybercentreCanada/assemblyline/issues) to make sure no one else is working on the same thing and that whatever you are going to build still fits with the vision of the system.
+
+## Git workflow
+
+- Clone the repo to your own account
+- Checkout and pull the latest commits from the master branch
+- Make a branch
+- Work in any way you like and make sure your changes actually work
+- When you're satisfied with your changes, create a pull requests to the main assemblyline repo
+
+#### Transfer your service repo
+If you've worked on a new service that you want to be included in the default service selection you'll have to transfer the repo into our control.
+
+#### You are not allowed to merge:
+
+Even if you try to merge in your pull request, you will be denied. Only a few people in our team are allowed to merge code into our repositories.
+
+We check for new pull requests every day and will merge them in once they have been approved by someone in our team.