Inform the user that there is no explicit documentation

docs/README.md

@@ -0,0 +1,10 @@
+It might seem like that this directory contains documentation. However, that is
+not the case at the moment (I did not manage to persuade Sphinx to produce
+reasonable output). Please read the
+[thesis](https://gitea.ledoian.cz/LEdoian/bc_thesis) for overview and the many
+comments and docstrings in the source code for details.
+
+The fourth chapter of the thesis provides a guide to use Birdvisu, the third
+describes the design.
+
+Sorry for the inconvenience.