Doc updates.
* jc/grammo-fixes:
doc: grammofix in git-diff-tree
tutorial: grammofix
This means "show everything that is reachable from either one, but
exclude anything that is reachable from both of them".
- Please note that these range notation can be used with both `gitk`
-Please note that these range notations can be used with both gitk
-and "git log".
++Please note that these range notations can be used with both `gitk`
+and `git log`.
After inspecting what Bob did, if there is nothing urgent, Alice may
decide to continue working without pulling from Bob. If Bob's history