build PyPy wheels on GHA; update installation docs

Author: nulano

.github/workflows/test-windows.yml

@@ -88,7 +88,7 @@ jobs:
 
     # GPL licensed; skip if building wheels
     - name: Build dependencies / libimagequant
-      if: "github.event_name != 'push' || contains(matrix.python-version, 'pypy')"
+      if: "github.event_name != 'push'"
       run: "& winbuild\\build\\build_dep_libimagequant.cmd"
 
     # Raqm dependencies
@@ -143,14 +143,14 @@ jobs:
 
     - name: Build wheel
       id: wheel
-      if: "github.event_name == 'push' && !contains(matrix.python-version, 'pypy')"
+      if: "github.event_name == 'push'"
       run: |
         for /f "tokens=3 delims=/" %%a in ("${{ github.ref }}") do echo ::set-output name=dist::dist-%%a
         winbuild\\build\\build_pillow.cmd bdist_wheel"
       shell: cmd
 
-    - uses: actions/upload-artifact@v2-preview
-      if: "github.event_name == 'push' && !contains(matrix.python-version, 'pypy')"
+    - uses: actions/upload-artifact@v2
+      if: "github.event_name == 'push'"
       with:
         name: ${{ steps.wheel.outputs.dist }}
         path: dist\*.whl

docs/installation.rst

@@ -292,7 +292,10 @@ or from within the uncompressed source directory::
 Building on Windows
 ^^^^^^^^^^^^^^^^^^^
 
-There are build scripts and notes for the Windows build in the ``winbuild`` directory.
+We recommend you use prebuilt wheels from PyPI.
+If you wish to compile Pillow manually, you can use the build scripts
+in the ``winbuild`` directory used for CI testing and development.
+These scripts require Visual Studio 2017 or newer and NASM.
 
 Building on FreeBSD
 ^^^^^^^^^^^^^^^^^^^