readme: update git commands for ahead/behind arrows

README.md

@@ -910,10 +910,10 @@ feature:master wip ⇣42⇡42 ⇠42⇢42 *42 merge ~42 +42 !42 ?42
 | `feature` | current branch; replaced with `#tag` or `@commit` if not on a branch | `git status --ignore-submodules=dirty`                 |
 | `master`  | remote tracking branch; only shown if different from local branch    | `git rev-parse --abbrev-ref --symbolic-full-name @{u}` |
 | `wip`     | the latest commit's summary contains "wip" or "WIP"                  | `git show --pretty=%s --no-patch HEAD`                 |
-| `⇣42`     | this many commits behind the remote                                  | `git status --ignore-submodules=dirty`                 |
+| `⇣42`     | this many commits behind the remote                                  | `git rev-list --right-only --count HEAD...@{upstream}` |
-| `⇡42`     | this many commits ahead of the remote                                | `git status --ignore-submodules=dirty`                 |
+| `⇡42`     | this many commits ahead of the remote                                | `git rev-list --left-only --count HEAD...@{upstream}`  |
-| `⇠42`     | this many commits behind the push remote                             | `git rev-list --left-right --count HEAD...@{push}`     |
+| `⇠42`     | this many commits behind the push remote                             | `git rev-list --right-only --count HEAD...@{push}`     |
-| `⇢42`     | this many commits ahead of the push remote                           | `git rev-list --left-right --count HEAD...@{push}`     |
+| `⇢42`     | this many commits ahead of the push remote                           | `git rev-list --left-only --count HEAD...@{push}`      |
 | `*42`     | this many stashes                                                    | `git stash list`                                       |
 | `merge`   | repository state                                                     | `git status --ignore-submodules=dirty`                 |
 | `~42`     | this many merge conflicts                                            | `git status --ignore-submodules=dirty`                 |