Fix typo in src/etc/htmldocck.py

Co-authored-by: León Orell Valerian Liehr <[email protected]>

Author: Derukugis

src/etc/htmldocck.py

@@ -2,7 +2,7 @@
 # -*- coding: utf-8 -*-
 
 r"""
-For docmentation and usage instructions, please see
+For documentation and usage instructions, please see
 https://rustc-dev-guide.rust-lang.org/rustdoc-internals.html#dotting-is-and-crossing-ts
 
 htmldocck.py is a custom checker script for Rustdoc HTML outputs.