docs/man/mangen.go: move fmt.Fprintf to infof
docs/man/mangen.go: move fmt.Fprintf to infof

For non-fatal warning messages, let's move all calls to fmt.Fprintf into
a wrapper function called 'infof' that behaves identically.

In a subsequent commit, calls to this function will be guarded by a
--verbose check, to ensure that we are not logging too much.

github/git-lfs,github/git-lfs,github/git-lfs