README: Add License.

README.md

@@ -9,3 +9,81 @@ functions more comfortable in Typed Racket.
 
 This package is distributed under the [GNU GPLv3
 licence](https://www.gnu.org/licenses/quick-guide-gplv3.html).
+
+# Contributing
+
+Contributions, comments, bug reports, etc. are very welcome!
+
+For [ethical
+reasons](https://en.wikipedia.org/wiki/Embrace,_extend,_and_extinguish),
+I prefer not to host this package on
+[GitHub](https://en.wikipedia.org/wiki/GitHub#Acquisition_by_Microsoft).
+Luckily, Git allows creating and submitting patches by E-mail in very
+easily.  Here is a simple workflow that you can use to contribute to
+this library.
+
+## Submit patches
+
+Start by checking out this repository:
+
+```
+git clone https://git.marvid.fr/scolobb/typed-compose.git
+cd typed-compose
+```
+
+Start a new branch `my-contribution` for you contribution:
+
+```
+git checkout -b my-contribution
+```
+
+Hack hack hack, do a couple commits, maybe take a look at a list of
+the commits your branch `my-contribution` contains:
+
+```
+git log --pretty=oneline master..my-contribution
+```
+
+Now create one patch file for every commit added to branch
+`my-contribution`, which is new with respect to `master`:
+
+```
+git format-patch master
+```
+
+This should produce one patch file for commit,
+e.g. `0001-Commit-1.patch`, `0002-Commit-2.patch`, etc.  Send all of
+these files to me to `scolobb` at `marvid.fr`, or to any other address
+you think you can contact me at.  I will give you feedback and we will
+work together towards getting your changes in, which is a fancy way of
+saying that I will probably take in your changes without too much
+hassle if they follow some very basic style guidelines.  Speaking of
+which:
+
+## Style guidelines
+
+When submitting changes, try to make it as similar as possible in
+style to the existing code, which approximately follows the style used
+across the Racket code base. If you use Emacs with Racket Mode or
+DrRacket, you should be fine with default settings.
+
+When adding new code, please consider updating the Scribble
+documentation `manual.scrbl` accordingly.  I believe that good
+documentation is more important than good code, because with good docs
+you can at least know how to fix the whole thing.
+
+## License
+
+This program is free software: you can redistribute it and/or modify it under
+the terms of the GNU General Public License as published by the Free Software
+Foundation, either version 3 of the License, or (at your option) any
+later version.
+
+This program is distributed in the hope that it will be useful, but
+**without any warranty**; without even the implied warranty of
+**merchantability** or **fitness for a particular purpose**.  See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License along with
+this program.  If not, see
+[https://www.gnu.org/licenses/](https://www.gnu.org/licenses/).