Add note which ones are emojis

Author: derickr

reference/pcre/pattern.syntax.xml

@@ -840,7 +840,7 @@
      <row rowsep="1">
       <entry><literal>So</literal></entry>
       <entry>Other symbol</entry>
-      <entry></entry>
+      <entry>Includes emojis</entry>
      </row>
      <row>
       <entry><literal>Z</literal></entry>