docs: warn about special characters in passwords in .env.example

Docker Compose interprets $ as variable substitution in unquoted values.
Passwords containing $, &, # etc. must be wrapped in single quotes.

Authored by: Jack Levy

.env.example

@@ -17,7 +17,10 @@ ENCRYPTION_SECRET_KEY=
 
 # ─── PostgreSQL ───────────────────────────────────────────────────────────────
 POSTGRES_USER=congress
-POSTGRES_PASSWORD=congress
+# If your password contains special characters ($, &, #, etc.), wrap it in single quotes
+# to prevent Docker Compose from interpreting them as variable substitutions.
+# Example: POSTGRES_PASSWORD='p@$$w0rd&safe'
+POSTGRES_PASSWORD=change-me
 POSTGRES_DB=pocketveto
 
 # These are constructed automatically from the above in docker-compose.yml.