update CONTRIBUTING.md with a requirement for Docker Compose `name` property (#235)

Apps/Mongo/docker-compose.yml

@@ -1,4 +1,4 @@
-name: MongoDB
+name: mongodb
 services:
   mongo:
     image: mongo:6.0.6

CONTRIBUTING.md

@@ -39,7 +39,9 @@ App-Name
 
 Each directory under [Apps](Apps) correspond to a CasaOS App. The directory should contain at least a `docker-compose.yml` file:
 
-- It should be a valid [Docker Compose file](https://docs.docker.com/compose/compose-file/).
+- It should be a valid [Docker Compose file](https://docs.docker.com/compose/compose-file/). Here are some requirements (but not limited to):
+
+  - `name` must contain only lower case letters, numbers, underscore "`_`" and hyphen "`-`" (in other words, must match `^[a-z0-9][a-z0-9_-]*$`)
 
 - Image tag should be specific, e.g. `:0.1.2`, instead of `:latest`.
 
@@ -137,18 +139,13 @@ Each directory under [Apps](Apps) correspond to a CasaOS App. The directory shou
 
         For resolves some cases. Casaos provide some magic value to power your application:
 
-        - Any environment variable that user to set
+        - Environment variable
-        - $WEBUI_PORT
-
-        ##### Environment variable
-        > for developer
 
             your application can read environment variable that user set, such as `OPENAI_API_KEY` from environment variable. It is store in `/etc/casaos/env`. User can set only once and using anywhere. It can be change by api, after change, all application will re up to inject new env var.
 
             **Note**: change the config didn't change the env var of current container. To set env var, you should use cli to set it.
 
-        #### WEBUI_PORT
+        - `WEBUI_PORT`
-        > for application maintainer
 
             your `docker-compose.yml` can use `WEBUI_PORT` to set webui port. Casaos will assign a available port for your application. You can use it like this:
 
@@ -167,7 +164,9 @@ Each directory under [Apps](Apps) correspond to a CasaOS App. The directory shou
             ...
                 port_map: ${WEBUI_PORT}
             ```
+
             or
+
             ```yaml
             ...
             ports: