fix comment issue

The "--" will cause the docker compose fail to start with below error message:

homepage  | chown: optional,: No such file or directory
homepage  | chown: your: No such file or directory
homepage  | chown: user: No such file or directory
homepage  | chown: id:1000: No such file or directory
homepage  | chown: --: No such file or directory
homepage  | chown: optional,: No such file or directory
homepage  | chown: your: No such file or directory
homepage  | chown: group: No such file or directory
homepage  | chown: id: No such file or directory
homepage exited with code 1

README.md

@@ -70,8 +70,8 @@ services:
     image: ghcr.io/gethomepage/homepage:latest
     container_name: homepage
     environment:
-      PUID: 1000 -- optional, your user id
-      PGID: 1000 -- optional, your group id
+      PUID: 1000 # optional, your user id
+      PGID: 1000 # optional, your group id
     ports:
       - 3000:3000
     volumes: