Fix a typo [ci skip]

znz · znz · commit f2377e4caafd · 2022-04-07T16:47:07.000+09:00
diff --git a/doc/documentation_guide.rdoc b/doc/documentation_guide.rdoc
@@ -62,7 +62,7 @@ involving new files <tt>doc/*.rdoc</tt>:
 
 - For a method, things are different.
   Documenting a method as above disables the "click to toggle source" feature
-  in the rendered documentaion.
+  in the rendered documentation.
 
   Therefore it's best to use file inclusion:
 
