Fix typos in git_tips.md doc.

docs/git_tips.md

 # Git Tips
 
 When using Git, there are a few tips that are particularly useful when working
 on the Chromium codebase, especially due to its size.
 
 [TOC]
 
 ## Remember the basic git convention:
 
     git COMMAND [FLAGS] [ARGUMENTS]
 
 Various git commands have underlying executable with a hyphenated name, such as
 `git-grep`, but these can also be called via the `git` wrapper script as
 `git grep` (and `man` should work either way too).
 
 ## Git references
 
 The following resources can provide background on how Git works:
 
 *   [Git-SVN Crash Course](http://git-scm.com/course/svn.html) -- this crash
-    course is useful for Subversion users  witching to Git.
+    course is useful for Subversion users switching to Git.
 *   [Think Like (a) Git](http://think-like-a-git.net/) -- does a great job of
     explaining the main purpose of Git operations.
 *   [Git User's Manual](http://schacon.github.com/git/user-manual.html) -- a
     great resource to learn more about ho to use Git properly.
 *   [A Visual Git Reference](http://marklodato.github.com/visual-git-guide/index-en.html)
-    -- a resource that explains various Git operations for visual reasons.
+    -- a resource that explains various Git operations for visual learners.
 *   [Git Cheat Sheet](http://cheat.errtheblog.com/s/git) -- now that you
     understand Git, here's a cheat sheet to quickly remind you of all the
     commands you need.
 
 ## Committing changes
 
 For a simple workflow (always commit all changed files, don't keep local
 revisions), the following script handles check; you may wish to call it `gci`
 (git commit) or similar.
 
@@ skipping 78 matching lines @@
 
     '\,//, ! s/foo/bar/g'
 
 ## Diffs
 
     git diff --shortstat
 
 Displays summary statistics, such as:
 
     2104 files changed, 9309 insertions(+), 9309 deletions(-)