Create web-ready version of "How to contribute code"

content/essential-knowledge/how-to-contribute-code.md

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+# A guide on how to contribute code
+
+Welcome! If you're new to GitHub and open source, it can seem quite difficult to get started.
+Here is a step-by-step guide on how to contribute code to the SourceBots project!
+
+## How to set up GitHub
+[Create a GitHub account](https://github.com/join), or log in if you already have an account.
+
+It's useful to stay logged in, so it's as easy as possible to keep up to date and make contributions.
+
+## How to choose something to work on
+Have a look at [TODO: find page]
+
+## Encouragement to make small changes
+We encourage you to make any changes, however small. e.g. if you spot a spelling error somewhere, why not fix it and make a pull request? This is a good way to familiarise yourself with the process, and is a good stepping stone towards larger contributions.
+
+## How to make a small change (e.g. to website / docs) using GitHub online editor: 
+
+Suppose you have a file you'd like to change. Then,
+
+TODO: *all* the steps. Make a commit to a new branch, submit a PR. In detail, for people who have never used git.
+
+* becoming a member of SourceBots organisation
+* setting up a new branch on the SourceBots repo (not creating a fork)
+- or, depending on our contribution system, creating a fork.
+* making an edit (with the pencil icon) -> set up a new branch, if you haven't already.
+Naming the branch. 
+You can't push to master.
+This might create a fork automatically for you if you're not a member of the [SourceBots organisation](https://github.com/sourcebots).
+* committing the changes (with meaningful commit message + description)
+* adding more changes to your branch (flat structure: don't create a sub-branch (terminology?) and do a PR from sub-branch -> your new branch?)
+* creating a pull request (TODO: when?)
+* waiting for someone to review your code (and/or asking for feedback, perhaps on the slack)
+* committing more changes, completing the review process
+
+TODO: put these TODOs in more appropriate places other than in the document itself?
+
+TODO: link to a good guide (with more detail) about this. But it's good to have our own version for making minimal commits and PRs for *our* specific workflow. It's also a useful way for people like myself to learn by writing.
+
+TODO: include *tip* boxes? For tangential but useful information/explanation about the general principles behind e.g. commits, forks, branches, and more complete guides/exceptions about when to do different things. (Or, in another style? By an example of a project with good documentation)
+
+## How to set up git on your local machine
+To make more advanced changes, it may be necessary to install and set up git on your local machine.
+To install git, see https://git-scm.com/book/en/v2/Getting-Started-Installing-Git.
+
+TODO:
+
+* adding ssh keys, where relevant
+* adding GitHub auth tokens, where relevant
+* ? does the GitHub desktop app, or GitKraken, or other IDEs guide you through this process well? Subsections maybe
+
+## Using git by CLI / GitHub desktop app (e.g. adding some code)
+TODO:
+
+* setting up a new branch on the SourceBots repo (not creating a fork)
+* how to make a commit
+* how to push to a branch
+
+
+## Conventions for PRs, commits, comments
+
+More advanced:
+
+* Code review (?)
+* Setting up dev environment