Add document about proxy settings to README.md

Author: sakama

README.md

@@ -14,7 +14,7 @@ Stores files on a SFTP Server
 ## Configuration
 
 - **host**: (string, required)
-- **port**: (string, default: `22`)
+- **port**: (int, default: `22`)
 - **user**: (string, required)
 - **password**: (string, default: `null`)
 - **secret_key_file**: (string, default: `null`) [see below](#secret-keyfile-configuration)
@@ -25,6 +25,19 @@ Stores files on a SFTP Server
 - **file_ext**: Extension of output files (string, required)
 - **sequence_format**: Format for sequence part of output files (string, default: `".%03d.%02d"`)
 
+### Proxy configuration
+
+- **proxy**:
+    - **type**: (string(http | socks | stream), required, default: `null`)
+        - **http**: use HTTP Proxy
+        - **socks**: use SOCKS Proxy
+        - **stream**: Connects to the SFTP server through a remote host reached by SSH
+    - **host**: (string, required)
+    - **port**: (int, default: `22`)
+    - **user**: (string, optional)
+    - **password**: (string, optional, default: `null`)
+    - **command**: (string, optional)
+    
 ## Example
 
 ```yaml
@@ -42,10 +55,31 @@ out:
   sequence_format: ".%01d%01d"
 ```
 
+With proxy
+```yaml
+out:
+  type: sftp
+  host: 127.0.0.1
+  port: 22
+  user: embulk
+  secret_key_file: /Users/embulk/.ssh/id_rsa
+  secret_key_passphrase: secret_pass
+  user_directory_is_root: false
+  timeout: 600
+  path_prefix: /data/sftp
+  proxy:
+    type: http
+    host: proxy_host
+    port: 8080
+    user: proxy_user
+    password: proxy_secret_pass
+    command:
+```
+
 ### Secret Keyfile configuration
 
 Please set path of secret_key_file as follows.
-```
+```yaml
 out:
   type: sftp
   ...
@@ -54,7 +88,7 @@ out:
 ```
 
 You can also embed contents of secret_key_file at config.yml.
-```
+```yaml
 out:
   type: sftp
   ...