Explain Git characters in man page

Fixes GH-778.

man/exa.1.md

@@ -183,6 +183,10 @@ These options are available when running with `--long` (`-l`):
 `--git`  [if exa was built with git support]
 : List each file’s Git status, if tracked.
 
+This adds a two-character column indicating the staged and unstaged statuses respectively. The status character can be ‘`-`’ for not modified, ‘`M`’ for a modified file, ‘`N`’ for a new file, ‘`D`’ for deleted, ‘`R`’ for renamed, ‘`T`’ for type-change, ‘`I`’ for ignored, and ‘`U`’ for conflicted.
+
+Directories will be shown to have the status of their contents, which is how ‘deleted’ is possible: if a directory contains a file that has a certain status, it will be shown to have that status.
+
 
 ENVIRONMENT VARIABLES
 =====================