AUTHORS.md: make clickable links

AUTHORS.md

@@ -1,4 +1,4 @@
-Gorka Lerchundi Osa (@glerchundi)
-Laurent Bercot (@skarnet)
-John Regan (@jprjr)
-Dreamcat4 (@dreamcat4)
+Gorka Lerchundi Osa ([@glerchundi](https://github.com/glerchundi))  
+Laurent Bercot ([@skarnet](https://github.com/skarnet))  
+John Regan ([@jprjr](https://github.com/jprjr))  
+Dreamcat4 ([@dreamcat4](https://github.com/dreamcat4))