Updated documentation for query string params.

httpie/cli.py

@@ -212,7 +212,8 @@ parser.add_argument(
         A key-value pair whose type is defined by the
         separator used. It can be an HTTP header (header:value),
         a data field to be used in the request body (field_name=value),
-        a raw JSON data field (field_name:=value),
+        a raw JSON data field (field_name:=value), 
+        a query parameter (name=:value),
         or a file field (field_name@/path/to/file).
         You can use a backslash to escape a colliding
         separator in the field name.