Add README file

- describe the project's goals
- contributions are welcome
- mention the GitFlow branching model

README.md

@@ -0,0 +1,30 @@
+# A Python library to study linear algebra
+
+The goal of the `lalib` project is to create
+    a library written in pure [Python](https://docs.python.org/3/)
+    (incl. the [standard library](https://docs.python.org/3/library/index.html))
+    and thereby learn about
+        [linear algebra](https://en.wikipedia.org/wiki/Linear_algebra)
+    by reading and writing code.
+
+
+## Contributing & Development
+
+This project is open for any kind of contribution,
+    be it by writing code for new features or bugfixes,
+    or by raising [issues](https://github.com/webartifex/lalib/issues).
+All contributions become open-source themselves, under the
+    [MIT license](https://github.com/webartifex/lalib/blob/main/LICENSE.txt).
+
+
+### Branching Strategy
+
+The branches in this repository follow the
+    [GitFlow](https://nvie.com/posts/a-successful-git-branching-model/) model.
+Feature branches are rebased onto
+    the [develop](https://github.com/webartifex/lalib/tree/develop) branch
+    *before* being merged.
+Whereas a rebase makes a simple fast-forward merge possible,
+    all merges are made with explicit and *empty* merge commits.
+This ensures that past branches remain visible in the logs,
+    for example, with `git log --graph`.