This was clearly intended for index, but because it was called "fish"
it was overwritten by the "fish" command man page.
I also added the tutorial and faq. Both of those might not be *ideal*
as man pages (the tutorial makes references to colors that won't show
up), but it's better to provide them than not.
Hat-tip to @wwared
See #5521.
[ci skip]
This runs build_tools/style.fish, which runs clang-format on C++, fish_indent on fish and (new) black on python.
If anything is wrong with the formatting, we should fix the tools, but automated formatting is worth it.
sphinx expects that the description for a command (as appearing in its man
page) be provided in conf.py, not in the rst file itself. LLVM handles this
with some custom Python code that parses it out of the file. Do the same
thing in fish.
