[css-text] Add reference

Author: frivoal

css-text-3/Overview.bs

@@ -1281,6 +1281,8 @@ Order of Operations</h4>
     Note: For HTML documents,
     carriage returns present in the source code
     are converted to line feeds at the parsing stage
+    (see [[HTML#preprocessing-the-input-stream]]
+    and the definition of [=normalize newlines=] in [[INFRA]])
     and therefore do no appear as U+000D to CSS.
     However, the character <em>is</em> preserved--
     and the above rule observable--