[gnome-builder] beautifier: Document from where are commands launched

[Christian Hergert <chergert src gnome org>]

commit 61fb707fd519cb9745e77a9ff2e9a792d5774e92
Author: vanadiae <vanadiae35 gmail com>
Date:   Sat Feb 6 23:44:22 2021 +0100

    beautifier: Document from where are commands launched

 src/plugins/beautifier/README.md | 1 +
 1 file changed, 1 insertion(+)
---
diff --git a/src/plugins/beautifier/README.md b/src/plugins/beautifier/README.md
index d3b24cdc0..4dff4e7be 100644
--- a/src/plugins/beautifier/README.md
+++ b/src/plugins/beautifier/README.md
@@ -105,6 +105,7 @@ or
   with pattern substitution:
       @s@ for the selected text put in a file.
       @c@ for the config file define by the config key.
+  Such commands are launched from the file's parent directory, which means that for file in src/foo/baz.c, 
the PWD will be src/foo/.
 
 By adding [internal] in front of the command pattern, the command is
 searched in the Builder data dir.