add options to log man page.
--- a/doc/hg.1.txt
+++ b/doc/hg.1.txt
@@ -376,7 +376,11 @@ log [-r revision ...] [-p] [files]::
options:
-I, --include <pat> include names matching the given patterns
-X, --exclude <pat> exclude names matching the given patterns
+ -b, --branch show branches
+ -k, --keyword <str> search for keywords
-l, --limit <num> print no more than this many changes
+ -M, --no-merges do not show merges
+ -m, --only-merges only show merges
-r, --rev <A> show the specified revision or range
-p, --patch show patch