Update TTS page to mention Text to Speech project setting

tutorials/audio/text_to_speech.rst

@@ -8,10 +8,19 @@ Basic Usage
 
 Basic usage of text-to-speech involves the following one-time steps:
 
+- Enable TTS in the Godot editor for your project
 - Query the system for a list of usable voices
 - Store the ID of the voice you want to use
 
-Once you have the voice ID, you can use it to speak some text:
+By default, the Godot project-level setting for text-to-speech is disabled, to avoid unnecessary overhead. To enable it:
+
+- Go to **Project > Project Settings**
+- Make sure the **Advanced Settings** toggle is enabled
+- Click on **Audio > General**
+- Ensure the **Text to Speech** option is checked
+- Restart Godot if prompted to do so.
+
+Text-to-speech uses a specific voice. Depending on the user's system, they might have multiple voices installed. Once you have the voice ID, you can use it to speak some text:
 
 .. tabs::
  .. code-tab:: gdscript GDScript
@@ -72,6 +81,13 @@ Distro-specific one-liners
 |                  |     pacman -S speech-dispatcher festival espeakup                                                         |
 +------------------+-----------------------------------------------------------------------------------------------------------+
 
+Troubleshooting
+---------------
+
+If you get the error `Invalid get index '0' (on base: 'PackedStringArray').` for the line `var voice_id = voices[0]`, check if there are any items in `voices`. If not:
+
+- All users: make sure you enabled **Text to Speech** in project settings
+- Linux users: ensure you installed the system-specific libraries for text to speech
 
 Best practices
 --------------