Document the flow of adding a package to Fuel

1) Description of workflow on adding Fuel packages
2) Add note regarding building of bootstrap.
3) Add note regarding packages for kickstart/preceed.

Change-Id: I3233c473a3a0663d636d616990dc054f4c5abb8c
Closes-Bug: #1269850
Merge "Document the flow of adding a package to Fuel"