git-merge(1): document diff-algorithm option to merge-recursive

Commit 07924d4 (diff: Introduce --diff-algorithm command line option
2013-01-16) added diff-algorithm as a parameter to the recursive merge
strategy but did not document it.  Do so.

Signed-off-by: John Keeping <john@keeping.me.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/merge-strategies.txt

@@ -48,6 +48,12 @@ patience;;
 	this when the branches to be merged have diverged wildly.
 	See also linkgit:git-diff[1] `--patience`.
 
+diff-algorithm=[patience|minimal|histogram|myers];;
+	Tells 'merge-recursive' to use a different diff algorithm, which
+	can help avoid mismerges that occur due to unimportant matching
+	lines (such as braces from distinct functions).  See also
+	linkgit:git-diff[1] `--diff-algorithm`.
+
 ignore-space-change;;
 ignore-all-space;;
 ignore-space-at-eol;;