Make gitpathspecs(7) tutorial/document

[LemmingAvalanche]

“pathspecs” is defined in the glossary. But it is a significant enough thing to get its own manual page.

You could then expand on the glossary by:

• Adding examples
• Make it more reference-friendly as a syntax lookup
  • In other words: not just... “In the long form, the leading colon : is followed by an open parenthesis (, a comma-separated list of zero or more "magic words", and a close parentheses ) … ”
  • … but also spell that out like :(<magic>)<path>

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There should be a gitpathspecs(7). Not just a glossary entry.

This sounds like a good #leftoverbits topic for new-ish people to
work on, with help from old timers? I do agree that the entry in
the glossary has grown to be way too big. The pathspec magic itself
should be mentioned there in the glossary, but the details of it
feels a bit too much and the topic probably deserves its own manual
page, just like gitrevisions(7) has one.

https://lore.kernel.org/git/xmqq4it3e1y7.fsf@gitster.g/#t