Small changes. Add GitHub buttons.

README.md

 * **No need to download apps!** MARTINS.js is a WebAR engine. It runs in web browsers. Users can access the AR experience immediately.
 * **Fast and powerful!** MARTINS.js is GPU-accelerated. It uses WebGL2 and WebAssembly for turbocharged performance.
 * **No need of custom hardware or software!** MARTINS.js is built from scratch using standard web technologies. All it requires is a modern and compatible web browser.
-* **Fully standalone!** MARTINS.js has in it everything it needs to analyze the environment and help you create AR. There are no additional requirements.
+* **Fully standalone!** MARTINS.js has in it everything it needs to analyze the environment and help you create AR. There are no additional requirements. It's not WebXR.
 * **Easy to get started!** MARTINS.js can be used with a `<script>` tag in your page. A static HTML page is enough to get started.
 
 ## Author

docs/getting-started/index.md

 # Welcome to MARTINS.js!
 
+<iframe src="https://ghbtns.com/github-btn.html?user=alemart&repo=martins-js&type=star&count=true&size=large" frameborder="0" scrolling="0" width="170" height="30" title="GitHub"></iframe> <iframe src="https://ghbtns.com/github-btn.html?user=alemart&repo=martins-js&type=watch&count=true&size=large&v=2" frameborder="0" scrolling="0" width="170" height="30" title="GitHub"></iframe>
+
 **MARTINS.js** is a GPU-accelerated Augmented Reality engine for the web. It's a standalone WebAR technology for creating AR experiences that run in web browsers. Users don't need specialized hardware nor dedicated software - only a modern and compatible web browser.
 
 [Get started with WebAR](./introduction.md){ .md-button .md-button--primary }
 * **No need to download apps!** MARTINS.js is a WebAR engine. It runs in web browsers. Users can access the AR experience immediately.
 * **Fast and powerful!** MARTINS.js is GPU-accelerated. It uses WebGL2 and WebAssembly for turbocharged performance.
 * **No need of custom hardware or software!** MARTINS.js is built from scratch using standard web technologies. All it requires is a modern and compatible web browser.
-* **Fully standalone!** MARTINS.js has in it everything it needs to analyze the environment and help you create AR. There are no additional requirements.
+* **Fully standalone!** MARTINS.js has in it everything it needs to analyze the environment and help you create AR. There are no additional requirements. It's not WebXR.
 * **Easy to get started!** MARTINS.js can be used with a `<script>` tag in your page. A static HTML page is enough to get started.
 
 [Check out my WebAR demos](../demos.md){ .md-button }