Document required git version

[lencioni]

git-describe was taught --abbrev=0 in 1.5.0:

https://github.com/git/git/blob/master/Documentation/RelNotes/1.5.0.txt

git-describe was taught --match in 1.5.5:

https://github.com/git/git/blob/master/Documentation/RelNotes/1.5.5.txt

I don't see anything else potentially weird in here, so I think it is
safe to proclaim that the minimum git version required to run these
commands is 1.5.5.

Documenting this minimum version required here should help people debug
possible issues and help maintainers of this project understand the
impacts of modifying these commands in the future.

[ljharb]

Perhaps here we could do a check for the git version, and log something to stderr about it, before proceeding to the curl/wget checks?

[lencioni]

I'm not entirely sure I follow.

Also, that seems to already include a git version check of sorts: https://github.com/creationix/nvm/blob/c874a174791265b3ab614ea270a84335a1013be0/install.sh#L91

[ljharb]

I think that check is just checking for "show-ref" support - when was that added?

[lencioni]

It looks like git-show-ref was added by 358ddb62cf in 2006, which appears to be first included by 1.4.4. The release notes don't go back that far though.

git/git@358ddb62cf

[ljharb]

I think an explicit version check would be nice - if you don't want to add it here, that's OK, this is still an improvement :-)

[lencioni]

I think I'll leave it out.