Fix link in introduction.md

Fix broken link.

Author: Amanda Butler

docs/introduction/introduction.md

@@ -6,7 +6,7 @@ Mbed OS is an open-source operating system for platforms using Arm microcontroll
 
 If you want to dive straight in:
 
-- The source code is available on [GitHub](www.github.com/ARMmbed/mbed-os) and on our [release page](https://os.mbed.com/releases/).
+- The source code is available on [GitHub](https://github.com/ARMmbed/mbed-os) and on our [release page](https://os.mbed.com/releases/).
 - Or [try our quick start](/docs/development/tutorials/mbed-os-quick-start.html).
 
 ### Source code and licensing