Ruby

Update yjit docs (#6548)

• The list of supported architectures was updated in
  https://github.com/ruby/ruby/commit/5ef048e5b1c3dd61adf782ace570bb0a1f9bb12f
  but the first paragraph wasn't updated.
• --yjit-trace-exits was missing from the command-line options
• Fixes some spacing issues
• Updates call threshold default to 10, verified in the code that's
  correct.
• Add code ticks around method names.
• Fix namespace of stats example