Add comment re. testing PyInstaller executables

.appveyor.yml

@@ -52,6 +52,9 @@ test_script:
   - |
     %PYTHON%\Scripts\tox.exe -e coverage
     %PYTHON%\Scripts\tox.exe -e pyinstaller
+    # To verify that the resultant PyInstaller-generated binary executes
+    # cleanly (i.e., that it terminates with an exit code of 0 and isn't
+    # failing due to import/packaging-related errors, etc.).
     dist\Tahoe-LAFS\tahoe.exe --version
 
 after_test:

.circleci/config.yml

@@ -106,6 +106,9 @@ jobs:
             ~/.local/bin/tox -e pyinstaller
 
       - run:
+          # To verify that the resultant PyInstaller-generated binary executes
+          # cleanly (i.e., that it terminates with an exit code of 0 and isn't
+          # failing due to import/packaging-related errors, etc.).
           name: "Test PyInstaller executable"
           command: |
             dist/Tahoe-LAFS/tahoe --version

.travis.yml

@@ -29,6 +29,9 @@ script:
     else
       tox -e ${T}
     fi
+    # To verify that the resultant PyInstaller-generated binary executes
+    # cleanly (i.e., that it terminates with an exit code of 0 and isn't
+    # failing due to import/packaging-related errors, etc.).
     if [ "${T}" = "pyinstaller" ]; then dist/Tahoe-LAFS/tahoe --version; fi
 
 after_success: