cheat-sheet.md: Fix 'Incorperate' -> 'Incorporate' typo

cheat-sheet.md: Fix 'Incorperate' -> 'Incorporate' typo

This fixes a typo introduced by 36d8c70 (cheet-sheet.md: Add a
Git-specific cheat sheet, 2013-06-10).

We saw branched development earlier with mit-license and bsd-license,
where we used branches to isolate new feature development in a series
of related commits.  I've put this commit in a new branch as well,
based on the v1.0 commit:

  $ git checkout -b v1.x v1.0

After checking out the new branch, I fixed the typo in cheat-sheet.md
using my text editor.  Then staging and committing was the usual:

  $ git add cheat-sheet.md
  $ git commit --all --verbose

The reason for branching here is slightly different.  In the license
case, we weren't sure if the branch would land in master at all, so we
created experimental "feature branches".  Now we're confident that the
commit will land in master (the focus of future development), but we
think the branch may *also* be useful to folks using the version 1.0
release that aren't quite ready for the upgrades introducted in
97941bc (cheat-sheet.md: Mention 'config', 'diff', 'branch', 'remote',
..., 2013-06-10).  By creating a "maintenance branch" based on the
v1.0 commit, we can provide the fix both to the bleeding edge and
stable release users, ending up with something like:

  $ git log --graph --topo-order --oneline --decorate --all
  *   YYYYYYY Merge branch 'v1.x'
  |\
  | * XXXXXXX (tag: v1.1, v1.x) cheat-sheet.md: Fix 'Incorperate' -> 'Incorporate' typo
  * | 97941bc (master) cheat-sheet.md: Mention 'config', 'diff', 'branch', 'remote', ...
  |/
  * 36d8c70 (tag: v1.0) cheet-sheet.md: Add a Git-specific cheat sheet
  *   3ba6fc9 (public/master) Merge branch 'mit-license'
  ...

Where the v1.1 tag is going to come from a:

  $ git tag v1.1

after I stop editing this commit message for XXXXXXX, and YYYYYYY is
going to merge the v1.x branch into master.

Maintenance branches allow you to fix bugs in earlier versions of your project, and easily incorperate thos