Add initial README.

README.md

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+# Godot TTS
+
+This addon was primarily developed for the [Godot Accessibility addon](https://github.com/lightsoutgames/godot-accessibility), but should work well in other contexts where a Godot game might require text-to-speech.
+
+## Supported Platforms
+
+Text-to-speech is complicated, and some features may not work everywhere. Most optional features have an associated boolean property used to determine if the feature is available. Further, while I do attempt to ensure that this addon works as well as possible on all platforms, there may be bugs, and pull requests are welcome. Known supported platforms include:
+
+* Windows
+  * Screen readers via [Tolk](https://github.com/dkager/tolk/)
+  * Native WinRT
+* Linux via [Speech Dispatcher](https://freebsoft.org/speechd)
+* HTML 5
+* Android
+
+## Features
+
+* Speaking text, with interruption support on most platforms
+* Stopping speech in progress
+* Getting and setting speech rate in both native synthesizer units and percentages
+* Detecting whether a screen reader is active
+
+## API
+
+The public-facing API is contained entirely within [TTS.GD](TTS.GD).
+
+## Download
+
+Download the [latest release](https://github.com/lightsoutgames/godot-tts/releases).