docs(git-prompt): explain stashed icon (⚑) (#9619)

Stashed icon was added in #4880

plugins/git-prompt/README.md

@@ -24,6 +24,7 @@ The prompt may look like the following:
 - `(master|✖2✚3)`: on branch `master`, 2 conflicts, 3 files changed
 - `(experimental↓2↑3|✔)`: on branch `experimental`; your branch has diverged by 3 commits, remote by 2 commits; the repository is otherwise clean
 - `(:70c2952|✔)`: not on any branch; parent commit has hash `70c2952`; the repository is otherwise clean
+- `(master|⚑2)`: on branch `master`, there are 2 stashed changes
 
 ## Prompt Structure
 
@@ -43,6 +44,7 @@ The symbols are as follows:
 | ●n     | there are `n` staged files     |
 | ✖n     | there are `n` unmerged files   |
 | ✚n     | there are `n` unstaged files   |
+| ⚑n     | there are `n` stashed changes  |
 | …      | there are some untracked files |
 
 ### Branch Tracking Symbols