Mark website as generated for GitHub

Author: lpil

.gitattributes

@@ -1,5 +1,3 @@
-examples/* linguist-documentation=false
-
 # We want fancy syntax highlighting on GitHub, though GitHub doesn't know how
 # to speak Gleam. Until it does (maybe one day!) we'll tell GitHub that these
 # files are Rust, which has a similar enough syntax for the highlighting to
@@ -11,3 +9,4 @@ examples/* linguist-documentation=false
 
 # Erlang files generated by the Gleam compiler
 */gen/*/*.erl linguist-generated=true
+/docs/**/* linguist-generated=true