Adding notes on PATCH to the upgrade guide.

Discusses compatibility between PATCH and PUT, as well as how to add
support for JSON PATCH to your application.

Fixes #10439.
Fxied some typos
Merge pull request #10597 from steveklabnik/patch_documentation

Adding notes on PATCH to the upgrade guide. [ci skip]
Merge pull request #10678 from prathamesh-sonpatki/typos

Fixed some typos