Update docs to reference pages templates

• Documents Feature Pages
• Follow-up from: https://gitlab.com/gitlab-org/gitlab-ce/issues/47857 / https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/24760

New doc or update?

• New documentation
• Update existing documentation: https://docs.gitlab.com/ee/user/project/pages/getting_started_part_two.html

Checklists

Product Manager

• Add the correct labels
• Add the correct milestone
• Indicate the correct document/directory for this feature
• Fill the doc blurb below

Documentation blurb

We need to update the https://docs.gitlab.com/ee/user/project/pages/getting_started_part_two.html#project with a third, preferred option: using a template. The top Pages 5 (by stars) templates are included in the "from template" option in new project setup. Those can be easily selected.

If a different template is wanted, they will need to follow the https://docs.gitlab.com/ee/user/project/pages/getting_started_part_two.html#fork-a-project-to-get-started-from guidance.

Developer

• Copy the doc blurb above and paste it into the doc
• Write the tutorial - explain how to use the feature
• Submit the MR using the appropriate MR description template