Add contributing guide

CONTRIBUTING.md

@@ -0,0 +1,12 @@
+# Contributors guide
+Contributions are very welcome - both issues and pull requests! Please mention in your pull request that you release your work under the MPL-2.0 (see below).
+
+It may take up to 2 weeks at times for me to respond to issues and pull requests. If it has been a few days and you have not received a reply, consider joining [the Gitter/Matrix chat](https://app.gitter.im/#/room/#Pepperminty-Wiki_Lobby:gitter.im) and poking me on there.
+
+I recommend checking on your pull request or issue every few days for a reply.
+
+If you open a pull request, I will review your changes and reply with a review detailing some changes I would like you to make. It may take a few back and forth comments, but then once I am happy with your changes I'll accept them and merge them into the codebase. This way we can polish your contribution to make it fit in with the existing codebase better ✨
+
+It is also unlikely, but possible I may reject your changes. If this is the case, I will leave a comment explaining why.
+
+If you are no longer interested in continuing to work with a pull request or will be away for a while, please leave a comment. Nobody will be offended! If you do not leave a comment or do not respond for 2 weeks, I may take over your pull request, work on it, and merge it myself.

README.md

@@ -76,6 +76,8 @@ If you would like to encrypt any communications with me, you can find my GPG key
 ## Contributing
 Contributions are very welcome - both issues and pull requests! Please mention in your pull request that you release your work under the MPL-2.0 (see below).
 
+See [CONTRIBUTING.md](./CONTRIBUTING.md) for a guide on what to expect when submitting a pull request or issue to this project.
+
 If you're feeling that way inclined, the sponsor button at the top of the page (if you're on GitHub) will take you to my [Liberapay profile](https://liberapay.com/sbrl) if you'd like to donate to say an extra thank you :-)