Merge pull request #1231 from franmomu/patch-2

Update orientation documentation

Resources/doc/filters/orientation.rst

@@ -32,6 +32,10 @@ Example configuration:
 
     This filter should be called as early as possible to get the best results.
 
+.. caution::
+
+    This filter requires to have exif extension installed in order to work.
+
 
 .. _filter-rotate:
 
@@ -108,4 +112,4 @@ Flip Options
 
 
 .. _`BoxInterface`: http://imagine.readthedocs.io/en/latest/usage/coordinates.html#boxinterface
-.. _`Imagine Library`: http://imagine.readthedocs.io/en/latest/
+.. _`Imagine Library`: http://imagine.readthedocs.io/en/latest/