documentation about render textfield is added

README.md

@@ -88,6 +88,17 @@ rJS(window)
 
 * 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">`
 
   for integer step=1 is set by default