add get_binding_text() for script api

doc/en/scripting/user-input.md

@@ -60,6 +60,12 @@ input.get_bindings() -> strings array
 
 Returns all binding names.
 
+```python
+input.get_binding_text(bindname: str) -> str
+```
+
+Returns text representation of button by binding name.
+
 ```python
 input.is_pressed(code: str) -> bool
 ```