Update git-log.md

adds the command for displaying a detailed git history of a particular file or folder

pages/common/git-log.md

@@ -4,4 +4,8 @@
 
 - Show a history of commits
 
-`git log`
+`git log`
+
+- Show the history of a particular file or directory, including differences
+
+`git log -p PATH`