Fix Spelling and Grammar errors.
- Fix one spelling error and one grammar error on Installation
- Add 'so' to clarify the meaning of the first bullet on Preparing Your
  Application
- Fix two spelling errors, add missing words, and change authorize to
  authorise for normalization on Preparing Your Application
- Fix spelling errors on Authentication & Authorisation
- Fix spelling errors in Cold Start
Merge pull request #14 from NanoXD/Spell-Fix

Fix Spelling and Grammar errors.