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/install.rst

@@ -0,0 +1,80 @@
+Install
+=======
+
+Installing pre-built packages (Linux-only)
+------------------------------------------
+
+If you have a Linux system you may install the ``deltachat`` binary "wheel" packages
+without any "build-from-source" steps.
+Otherwise you need to `compile the Delta Chat bindings yourself`__.
+
+__ sourceinstall_
+
+We recommend to first create a fresh Python virtual environment
+and activate it in your shell::
+
+    python -m venv env
+    source env/bin/activate
+
+Afterwards, invoking ``python`` or ``pip install`` only
+modifies files in your ``env`` directory and leaves
+your system installation alone.
+
+For Linux we build wheels for all releases and push them to a python package
+index. To install the latest release::
+
+    pip install deltachat
+
+To verify it worked::
+
+    python -c "import deltachat"
+
+.. _sourceinstall:
+
+Installing bindings from source
+-------------------------------
+
+Install Rust and Cargo first.
+The easiest is probably to use `rustup <https://rustup.rs/>`_.
+
+Bootstrap Rust and Cargo by using rustup::
+
+   curl https://sh.rustup.rs -sSf | sh
+
+Then clone the deltachat-core-rust repo::
+
+   git clone https://github.com/deltachat/deltachat-core-rust
+   cd deltachat-core-rust
+
+To install the Delta Chat Python bindings make sure you have Python3 installed.
+E.g. on Debian-based systems `apt install python3 python3-pip
+python3-venv` should give you a usable python installation.
+
+First, build the core library::
+
+   cargo build --release -p deltachat_ffi --features jsonrpc
+
+`jsonrpc` feature is required even if not used by the bindings
+because `deltachat.h` includes JSON-RPC functions unconditionally.
+
+Create the virtual environment and activate it::
+
+   python -m venv env
+   source env/bin/activate
+
+Build and install the bindings::
+
+   export DCC_RS_DEV="$PWD"
+   export DCC_RS_TARGET=release
+   python -m pip install ./python
+
+`DCC_RS_DEV` environment variable specifies the location of
+the core development tree. If this variable is not set,
+`libdeltachat` library and `deltachat.h` header are expected
+to be installed system-wide.
+
+When `DCC_RS_DEV` is set, `DCC_RS_TARGET` specifies
+the build profile name to look up the artifacts
+in the target directory.
+In this case setting it can be skipped because
+`DCC_RS_TARGET=release` is the default.