release: improve macos docs after macos tests

- build macos dmg
    - however, do not upload macos dmg to assets as it cannot be
      executed since the app and installer are not signed and notarized
- upload artifacts
- tested executable on macOS

installer/build_dmg.sh

@@ -0,0 +1,22 @@
+#!/bin/sh
+
+# Create a folder (named dmg) to prepare our DMG in (if it doesn't already exist).
+
+# https://www.pythonguis.com/tutorials/packaging-pyqt5-applications-pyinstaller-macos-dmg/
+
+mkdir -p dist/dmg
+# Empty the dmg folder.
+rm -r dist/dmg/*
+# Copy the app bundle to the dmg folder.
+cp -r "dist/extract_otp_secrets.app" dist/dmg
+# If the DMG already exists, delete it.
+test -f "dist/extract_otp_secrets.dmg" && rm "dist/extract_otp_secrets.dmg"
+create-dmg \
+  --volname "Extract OTP Secrets" \
+  --window-pos 200 120 \
+  --window-size 600 300 \
+  --icon-size 100 \
+  --hide-extension "extract_otp_secrets.app" \
+  --app-drop-link 425 120 \
+  "dist/extract_otp_secrets.dmg" \
+  "dist/dmg/"