Update Docker .env (#3576)

### What problem does this PR solve?


### Type of change

- [x] Documentation Update

docker/.env

@@ -1,5 +1,7 @@
 # The type of doc engine to use.
-# Supported values are `elasticsearch`, `infinity`.
+# Available options:
+# - `elasticsearch` (default) 
+# - `infinity` (https://github.com/infiniflow/infinity)
 DOC_ENGINE=${DOC_ENGINE:-elasticsearch}
 
 # ------------------------------
@@ -20,7 +22,7 @@ ES_HOST=es01
 ES_PORT=1200
 
 # The password for Elasticsearch. 
-# When updated, you must revise the `es.password` entry in  service_conf.yaml accordingly.
+# When updated, you must revise the `es.password` entry in service_conf.yaml accordingly.
 ELASTIC_PASSWORD=infini_rag_flow
 
 # The port used to expose the Kibana service to the host machine, 
@@ -85,7 +87,7 @@ RAGFLOW_IMAGE=infiniflow/ragflow:dev-slim
 # RAGFLOW_IMAGE=infiniflow/ragflow:dev
 # 
 # The Docker image of the dev edition includes:
-# - Embedded embedding models:
+# - Built-in embedding models:
 #   - BAAI/bge-large-zh-v1.5
 #   - BAAI/bge-reranker-v2-m3
 #   - maidalun1020/bce-embedding-base_v1
@@ -123,3 +125,8 @@ TIMEZONE='Asia/Shanghai'
 # Optimizations for MacOS
 # Uncomment the following line if your OS is MacOS:
 # MACOS=1
+
+# The maximum file size for each uploaded file, in bytes.
+# You can uncomment this line and update the value if you wish to change 128M file size limit
+# MAX_CONTENT_LENGTH=134217728
+