* replaces Dockerfile using bazel-based build system
This commit updates the Dockerfile to work with anki's bazel-based build
system.
The anki Dockerfile was originally added in
https://github.com/ankitects/anki/pull/753 back in September 2020. The
file was moved to `docs/Dockerfile` in
0d354da93a, with a note that the file had
to be updated to work with anki's updated build system. The file
`docs/Dockerfile` was removed in
7cd2e9618f.
* install setuptools and wheel + xkb libraries
* install anki virtual env in fresh base image
* move Dockerfile out of root directory
* add readme file for dockerized anki
