docs(docs-readme): clarify documentation readme (#4538)
docs(docs-readme): clarify documentation readme (#4538)

* docs(docs-readme): clarify documentation readme

I was confused what `mitmproxy Python package` meant. At first I did `pipx install mitmproxy`, but that didn't work. Then I realized I needed it as a library/module, not cli.

Changed `build.sh` to `build.py` since it was deleted on commit a7d1f32c89f3ea8b989a2d63fac13a44bc34f946

* Update README.md

Co-authored-by: Maximilian Hils <64b2b6d12bfe4baae7dad3d018f8cbf6b0e7a044@maximilianhils.com>
mhils/mitmproxy,mhils/mitmproxy,Kriechi/mitmproxy,Kriechi/mitmproxy,mitmproxy/mitmproxy,Kriechi/mitmproxy,mitmproxy/mitmproxy,mhils/mitmproxy,mhils/mitmproxy,mitmproxy/mitmproxy,mitmproxy/mitmproxy,mitmproxy/mitmproxy,mhils/mitmproxy,Kriechi/mitmproxy