Add available since tags for hints API docs

Author: Takenaka Simon

docs/docs/hints/api.md

@@ -114,6 +114,8 @@ introJs().addHints();
 
 Show the hint with given `hintId`.
 
+**Available since**: v2.4.0
+
 **Example:**
 ```javascript
 introJs().showHint(1);
@@ -125,6 +127,8 @@ introJs().showHint(1);
 
 Show all hints.
 
+**Available since**: v2.4.0
+
 **Example:**
 ```javascript
 introJs().showHints();