Explain why warnings happen on import in README

- Relates to #42.
- Bump CI Python versions to latest non-EOL Python 3.
- Drop Python2 from CI for now.

.github/workflows/build.yml

@@ -20,27 +20,29 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, macos-latest]
-        python-version: [2.7, 3.5, 3.6, 3.7, 3.8, 3.9, "3.10", pypy2, pypy3]
+        python-version: [3.8, 3.9, "3.10", "3.11", "3.12", "pypy3.9"]
         include:
           - os: windows-latest
             python-version: 3.9
           - os: windows-latest
             python-version: "3.10"
+          - os: windows-latest
+            python-version: "3.11"
+          - os: windows-latest
+            python-version: "3.12"
         exclude:
           - os: macos-latest
             python-version: 3.5
           - os: macos-latest
             python-version: 3.6
           - os: macos-latest
-            python-version: pypy2
-          - os: macos-latest
-            python-version: pypy3
+            python-version: "pypy3.9"
 
 
     steps:
-    - uses: actions/checkout@v2
+    - uses: actions/checkout@v3
     - name: Set up Python ${{ matrix.python-version }}
-      uses: actions/setup-python@v2
+      uses: actions/setup-python@v4
       with:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies

README.rst

@@ -805,6 +805,24 @@ A workaround helper script is provided, it may be executed like so:
 Further details on this topic may be found in the `manual optimization`_
 section of this document.
 
+WARNING: There are unused tokens on import
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+This indicates that the installation method or source for this package
+being imported isn't optimized.  A quick workaround is to follow the
+instructions at the `manual optimization`_ section of this document to
+ensure these messages are no longer generated (and if this warning
+happens every time the module is imported, it means the symbol tables
+are regenerated every time that happens and this extra computational
+overhead should be corrected through the generation of that optimization
+module).
+
+This optimization module is included with the wheel release and the
+source release on PyPI, but it is not part of the source repository as
+generated code are never committed.  Should a binary release made by
+a third-party results in this warning upon import, their release should
+be corrected to include the optimization module.
+
 Slow performance
 ~~~~~~~~~~~~~~~~