Add some extra detail to git log command

Added the useful —oneline flag and also info on how to quit out (since
I always forget).

pages/common/git-log.md

@@ -9,3 +9,11 @@
 - Show the history of a particular file or directory, including differences
 
 `git log -p PATH`
+
+- Show only the first line of each commits
+
+`git log --oneline`
+
+- Quit out of git log
+
+`q`