gh-pages (document release branch) should be automatically populated

[ashahi1]

Currently, any changes to [vmware]/docs has to be manually copied to gh-pages. The process should be automated - any changes to [vmware]/docs should be promoted to gh-pages automatically

https://github.com/vmware/docker-volume-vsphere/blob/master/CONTRIBUTING.md#documentation-pr

[pdhamdhere]

Changes should be promoted from master to gh-pages every time we cut release. And this is P0 and must be fixed before next release.

[shuklanirdesh82]

PR #1798 is bringing doc changes from vmware:master to vmware:gh-pages automatically.

Next step:

• 1. configure a vm to invoke cron job to run this script daily. (tracking at Configure a vm to invoke cron job for script - update_GHpages.sh #1854)

• 2. Remove instruction from https://github.com/vmware/docker-volume-vsphere/blob/master/CONTRIBUTING.md#documentation-pr

targeted work for Mufasa sprint is done and moving this issue to next sprint to have automated job.

[ashahi1]

Filed a separate issue for creating a cron job - #1854