feat(macros): add hint comments

info.toml

@@ -958,7 +958,12 @@ mode = "compile"
 hint = """
 You only need to add a single character to make this compile.
 The way macros are written, it wants to see something between each
-"macro arm", so it can separate them."""
+"macro arm", so it can separate them.
+
+That's all the macro exercises we have in here, but it's barely even
+scratching the surface of what you can do with Rust's macros. For a more
+thorough introduction, you can have a read through the little book of Rust
+macros: https://veykril.github.io/tlborm/"""
 
 # TEST 4