chore(.env.example): add comments for opendal (#11778)

Signed-off-by: -LAN- <laipz8200@outlook.com>

docker/.env.example

 # The type of storage to use for storing user files.
 STORAGE_TYPE=opendal
 
-# Apache OpenDAL Configuration, refer to https://github.com/apache/opendal
-# The scheme for the OpenDAL storage.
+# Apache OpenDAL Configuration
+# The configuration for OpenDAL consists of the following format: OPENDAL_<SCHEME_NAME>_<CONFIG_NAME>.
+# You can find all the service configurations (CONFIG_NAME) in the repository at: https://github.com/apache/opendal/tree/main/core/src/services.
+# Dify will scan configurations starting with OPENDAL_<SCHEME_NAME> and automatically apply them.
+# The scheme name for the OpenDAL storage.
 OPENDAL_SCHEME=fs
 # Configurations for OpenDAL Local File System.
 OPENDAL_FS_ROOT=storage
 
 # Proxy
 HTTP_PROXY=
-HTTPS_PROXY=
+HTTPS_PROXY=