add note about contributions

CONTRIBUTING.md

@@ -0,0 +1,16 @@
+# Contributing
+
+[ This is a placeholder, because it's early days and the volume of contributions thus far can be counted in an eggcup ]
+
+* Contributions are very welcome
+
+* Please open an issue (or otherwise establish some kind of dialogue) before you send a PR I haven't asked for.
+Just so I know it's expected and you're not wasting time doing something I won't accept or have already started on
+
+* The Nix code in Liminix is MIT-licenced (same as Nixpkgs), but the code it combines from other places (e.g. Linux, OpenWRT) may
+have a variety of licences.  I have no intention of asking for copyright assignment: just like when submitting to the
+Linux kernel you retain the copyright on the code you contribute.
+
+* Please govern yourself in Liminix project venues according to the guidance in the [geekfeminism "Community Anti-harassment Policy"](https://geekfeminism.wikia.org/wiki/Community_anti-harassment/Policy).
+
+* If you've read the preceding bullets and don't find anything to disagree with, open a PR

README.md

@@ -125,6 +125,20 @@ filesystem, and you can run `nix-store --query` on it:
     nix-store -q --tree manifest
 
 
+## Contributing
+
+Contributions are welcome, though in these early days there may be a
+bit of back and forth involved before patches are merged.  Have a read
+of [CONTRIBUTING](CONTRIBUTING.md) and [STYLE](STYLE.md) and try to
+intuit the unarticulated vision :-)
+
+Liminix' primary repo is https://gti.telent.net/dan/liminix. There's a
+[mirror on Github](https://github.com/telent/liminix) for convenience
+and visibility: you can open PRs against that but be aware that the
+process of merging them may be arcane. Some day, we will have
+federated Gitea using ActivityPub.
+
+
 ## Articles of interest
 
 * [Build Safety of Software in 28 Popular Home Routers](https://cyber-itl.org/assets/papers/2018/build_safety_of_software_in_28_popular_home_routers.pdf):