jump: fix issues in plugin and document CTRL+G key binding

- Fixes `readlink -e` dependency which isn't supported in macOS
  (fixes #3235).
- Uses native zsh wildcard expansion instead of calls to `ls`.
- Prepends commands with `command` and `builtin` to bypass aliases
  and functions.
- Documents CTRL+G key binding to substitute mark name in the command
  line with the mark path (https://github.com/ohmyzsh/ohmyzsh/pull/2045#issuecomment-22826540).