document editable mode installation in winbuild/build.rst

Author: nulano

winbuild/build.rst

@@ -87,11 +87,18 @@ are set by running ``winbuild\build\build_env.cmd`` and install Pillow with pip:
     winbuild\build\build_env.cmd
     python.exe -m pip install -v -C raqm=vendor -C fribidi=vendor .
 
+You can also install Pillow in `editable mode`_::
+
+    winbuild\build\build_env.cmd
+    python.exe -m pip install -v -C raqm=vendor -C fribidi=vendor -e .
+
 To build a wheel instead, run::
 
     winbuild\build\build_env.cmd
     python.exe -m pip wheel -v -C raqm=vendor -C fribidi=vendor .
 
+.. _editable mode: https://setuptools.pypa.io/en/latest/userguide/development_mode.html
+
 Testing Pillow
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