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)
 
 ---
 

src/more-information.md

@@ -0,0 +1,6 @@
+# Other places to find information
+
+You are going to find [Rustc API docs site] useful and there's more supplementary documentation in [Rust Forge].
+
+[Rustc API docs site]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc/
+[Rust Forge]: https://forge.rust-lang.org/