docs: generate deltachat-rpc-client documentation

To preview the docs, run:
```
scripts/build-python-docs.sh
firefox dist/html/index.html
```

I have removed the Makefile because modern Sphinx Makefile is just a
wrapper for `sphinx-build -M`:
3596590317/sphinx/templates/quickstart/Makefile.new_t
and sphinx-quickstart even has an option `--no-makefile`.
`make.bat` makes even less sense.
In `scripts/build-python-docs.sh` I use `sphinx-build` directly
without `make` wrapper.

python/doc/cffi/manylinux.rst

@@ -0,0 +1,25 @@
+Building Manylinux-Based Wheels
+===============================
+
+Building portable manylinux wheels which come with libdeltachat.so
+can be done with Docker_ or Podman_.
+
+.. _Docker: https://www.docker.com/
+.. _Podman: https://podman.io/
+
+If you want to build your own wheels, build container image first::
+
+   $ cd deltachat-core-rust # cd to deltachat-core-rust working tree
+   $ docker build -t deltachat/coredeps scripts/coredeps
+
+This will use the ``scripts/coredeps/Dockerfile`` to build
+container image called ``deltachat/coredeps``.  You can afterwards
+find it with::
+
+   $ docker images
+
+This docker image can be used to run tests and build Python wheels for all interpreters::
+
+    $ docker run -e CHATMAIL_DOMAIN \
+       --rm -it -v $(pwd):/mnt -w /mnt \
+       deltachat/coredeps scripts/run_all.sh