feat: add BSD and macos platforms to `--platform` option

[owenvoke]

Closes https://github.com/tldr-pages/tldr-python-client/issues/234 and closes https://github.com/tldr-pages/tldr-python-client/issues/235

[acuteenvy]

This doesn't work, because macos is not a directory. tldr --platform macos <page_name> always prints "documentation is not available".

There's also android, which isn't on the list here.

[owenvoke]

Ah, so we need to actually alias it. Will mark this as draft and work on the required changes.

I'll add Android as well. I feel like it's a bit redundant duplicating the platforms here though, so perhaps we can extract to a variable or something.

[kbdharun]

Hi, any updates on this?

[kbdharun]

Completed in #246