fix(docs): add required "inherits" option to example profile

Author: strager

src/doc/src/reference/config.md

@@ -118,6 +118,7 @@ offline = true              # do not access the network
 # Same keys as for [patch] in Cargo.toml
 
 [profile.<name>]         # Modify profile settings via config.
+inherits = "dev"         # If an option is missing, use dev's value.
 opt-level = 0            # Optimization level.
 debug = true             # Include debug info.
 split-debuginfo = '...'  # Debug info splitting behavior.