Merge pull request #7564 from nulano/config-docs

Use --config-settings in external libraries list in installation.rst

Author: hugovk

docs/installation.rst

@@ -151,13 +151,13 @@ Many of Pillow's features require external libraries:
 
   * Pillow has been tested with libjpeg versions **6b**, **8**, **9-9d** and
     libjpeg-turbo version **8**.
-  * Starting with Pillow 3.0.0, libjpeg is required by default, but
-    may be disabled with the ``--disable-jpeg`` flag.
+  * Starting with Pillow 3.0.0, libjpeg is required by default. It can be
+    disabled with the ``-C jpeg=disable`` flag.
 
 * **zlib** provides access to compressed PNGs
 
-  * Starting with Pillow 3.0.0, zlib is required by default, but may
-    be disabled with the ``--disable-zlib`` flag.
+  * Starting with Pillow 3.0.0, zlib is required by default. It can be
+    disabled with the ``-C zlib=disable`` flag.
 
 * **libtiff** provides compressed TIFF functionality