README.md: add links to ImageJ and SCIFIO code

Author: ctrueden

README.md

@@ -1,7 +1,8 @@
 SciJava Common is a common library for SciJava software. It provides a
 plugin framework, with an extensible mechanism for service discovery, driven
 by the SezPoz library, so that plugins can be loaded dynamically. It is used
-by both ImageJ and SCIFIO.
+by both [ImageJ](https://github.com/imagej/imagej) and
+[SCIFIO](https://github.com/scifio/scifio).
 
 This project also contains configuration files and scripts common to the
 SciJava software stack: