documentation about render textfield is added

README.md

@@ -87,6 +87,17 @@ rJS(window)
 ## rendering rules 
 
 * string json schema type is rendered as `<input type="string">`
+  
+  for multi-line textfield can be used contentMediaType = "text/plain" 
+  
+```json
+{
+  "type": "string",
+  "contentMediaType": "text/plain"
+}
+```
+
+  it is rendered as `<textarea></textarea>`
 
 * number/integer json schema type is rendered as `<input type="number">`