Add more info subsection with links to forge and rustc api docs

Author: spastorino

src/SUMMARY.md

@@ -1,6 +1,7 @@
 # Summary
 
-[About this guide](./about-this-guide.md)
+- [About this guide](./about-this-guide.md)
+    - [Other places to find information](./more-information.md)
 
 ---