Add .dockerignore to exclude secrets and cache

.dockerignore

@@ -0,0 +1,20 @@
+# Prevent secrets and junk from being baked into Docker images
+
+# Secrets
+.env
+.env.*
+
+# macOS junk
+.DS_Store
+
+# Python cache
+__pycache__/
+*.py[cod]
+
+# Virtual environments
+.venv/
+venv/
+
+# Git stuff (optional)
+.git
+.gitignore