Mention defusedxml

Co-authored-by: Ondrej Baranovič <[email protected]>

Author: radarhere

docs/installation.rst

@@ -42,9 +42,10 @@ Install Pillow with :command:`pip`::
     python3 -m pip install --upgrade pip
     python3 -m pip install --upgrade Pillow
 
-Optionally, install :pypi:`olefile` for Pillow to read FPX and MIC images::
+Optionally, install :pypi:`defusedxml` for Pillow to read XMP data,
+and :pypi:`olefile` for Pillow to read FPX and MIC images::
 
-    python3 -m pip install --upgrade olefile
+    python3 -m pip install --upgrade defusedxml olefile
 
 
 .. tab:: Linux