minor #9708 Note about relative file paths (xosofox)

This PR was submitted for the master branch but it was merged into the 2.7 branch instead (closes #9708).

Discussion
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Note about relative file paths

This fixes #9674.

Commits
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2a3b85a Note about relative file paths

Author: javiereguiluz

components/filesystem.rst

@@ -83,7 +83,7 @@ exists
 presence of one or more files or directories and returns ``false`` if any of
 them is missing::
 
-    // this directory exists, return true
+    // if this absolute directory exists, return true
     $fileSystem->exists('/tmp/photos');
 
     // rabbit.jpg exists, bottle.png does not exist, return false
@@ -93,6 +93,10 @@ them is missing::
 
     You can pass an array or any :phpclass:`Traversable` object as the first
     argument.
+    
+.. note::
+    If you are using non-absolute paths, the paths are relative to
+    the directory where the running PHP script is stored
 
 copy
 ~~~~