update doc

README.md

@@ -455,6 +455,8 @@ Http requests with url prefix `/news` and `/about` will be forwarded to **web02*
 
 frpc can connect frps using HTTP PROXY if you set os environment `HTTP_PROXY` or configure `http_proxy` param in frpc.ini file.
 
+It only works when protocol is tcp.
+
 ```ini
 # frpc.ini
 [common]

README_zh.md

@@ -472,6 +472,8 @@ locations = /news,/about
 
 可以通过设置 `HTTP_PROXY` 系统环境变量或者通过在 frpc 的配置文件中设置 `http_proxy` 参数来使用此功能。
 
+仅在 `protocol = tcp` 时生效。
+
 ```ini
 # frpc.ini
 [common]

conf/frpc_full.ini

@@ -6,6 +6,7 @@ server_addr = 0.0.0.0
 server_port = 7000
 
 # if you want to connect frps by http proxy, you can set http_proxy here or in global environment variables
+# it only works when protocol is tcp
 # http_proxy = http://user:pwd@192.168.1.128:8080
 
 # console or real logFile path like ./frpc.log