add some text about speech templates for Unicode chars in the mathml-docs repo

Author: NSoiffer

src/intent.html

@@ -204,6 +204,12 @@ <h3 id="mixing_intent_dictionaries">Intent Concept Dictionaries</h3>
     <p>Future versions of the <q>core</q> concept list may incorporate names
       from the <q>open</q> list if usage indicates that is appropriate.
      </p>
+
+    <p>There are thousands of Unicode characters that might be used in MathML.
+       As an aid to implementers, in the same repository there is a non-normative list of
+       <a href="https://w3c.github.io/mathml-docs/unicode-speech">speech templates</a> that provides
+       suggested speech for many of these characters.
+    </p>
   </section>
 
   <section>