More detailed paid time off policy
@pmachle1 reviewed our PTO policies, and noted that there was a gap between what is written in the handbook and what the law requires. See https://dev.gitlab.org/gitlab/organization/issues/367
With this merge request, we're creating a new page (https://about.gitlab.com/handbook/time-off) that holds the more detailed policies.
Additional edits need to be made to the Paid Time Off section of the main handbook in order to
- remove inconsistencies between the official full length policy and the short hand one
- link to the full length policies.