[Documentation] Moving product docs domain and GitHub repository

To maintain the growing documentation better and to have a dedicated site for it, the ERPNext product documentation/User Manual will be moved from:
Home to https://docs.erpnext.com.

To send documentation PRs, use the new repo which will be listed soon.

The shift will most likely be done by the end of this week. @saurabh6790.


The new site is: https://docs.erpnext.com/

GitHub repository: GitHub - frappe/erpnext_documentation: [DEPRECATED] ERPNext User Documentation. Please don't raise new contributions here.