Documentation/git-tools: improve discoverability of Git wiki

Documentation/git-tools: improve discoverability of Git wiki

These days, the best way to find Git-related tools is via a search
engine. The Git wiki may be a distant second, and git-tools.txt falls in
last place. Therefore, promote the Git wiki reference to the top of
git-tools.txt so the reader will encounter it first, rather than hiding
it away at the very bottom.

Signed-off-by: Eric Sunshine <redacted>
Signed-off-by: Junio C Hamano <redacted>