Documentation should list swig as a dependency

[sourcequench]

Foolish noobs like me will try the pip3 installation and fail with a 65-line error message and have to figure out what the issue is. Turns out, swig is a hard dependency in order to do the pip3 install, but it is not listed in the dependencies.

[explodeo]

I found that I needed the following installed to fix M2Crypto install errors:

• swig (as mentioned before)
• libssl-dev (openssl-devel for fedora)
• gcc
• python3 (I used 3.11)

Please add these to the documentation. It fixes the "legacy-install-error" thrown by the M2Crypto compilation portion of setup.py.