Update the FAQ:

• Change the frequency of snapshots from a day to a month
• Fix a missing closing parenthesis
• Add snapshot site http://snapshots.us.freebsd.org
• Generalize the paragraph about development branches
• Add an 18 months release interval for major versions and 8 months for minor versions
• Fix link for the PR query interface

PR: docs/115000
Submitted by: Ben Kaduk <minimarmot at gmail dot com>
Reviewed by: danger, trhodes
Approved by: gabor (mentor)