Updated update_revision.sh to use GitHub (#12)
Updated update_revision.sh to use GitHub (#12)

* Updated update_revision.sh to use GitHub

After updating the revision on the local sources file, the script now:
- Checks connection to GitHub
- Finds out if the sources file with the latest revision has been previously pushed
- Commits and pushes to the user's fork
- Creates a pull request on advancetoolchain/advance-toolchain GitHub repository, as long as a personal access token is supplied.

Usage text was improved accordingly.

Signed-off-by: Denilson Antonio Marques Junior <141e52e2d15e9d26cd1034b248c2a528d2241dad@linux.vnet.ibm.com>

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