Merge branch 'sn/doc-opt-notation' into maint

Merge branch 'sn/doc-opt-notation' into maint

* sn/doc-opt-notation:
  Fix {update,checkout}-index usage strings
  Put a space between `<' and argument in pack-objects usage string
  Remove stray quotes in --pretty and --format documentation
  Use parentheses and `...' where appropriate
  Fix odd markup in --diff-filter documentation
  Use angles for placeholders consistently