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).

plugins/jump/README.md

@@ -17,3 +17,15 @@ plugins=(... jump)
 | `mark [mark-name]`   | Create a mark with the given name or with the name of the current directory if none is provided |
 | `unmark <mark-name>` | Remove the given mark                                                                           |
 | `marks`              | List the existing marks and the directories they point to                                       |
+
+## Key bindings
+
+Pressing `CTRL`+`G` substitutes the written mark name for the full path of the mark.
+For example, with a mark named `mymark` pointing to `/path/to/my/mark`:
+```zsh
+$ cp /tmp/file mymark<C-g>
+```
+will become:
+```zsh
+$ cp /tmp/file /path/to/my/mark
+```