add a note about name changing the MASTER sessions to PRIMARY sessions.

i2p2www/pages/site/docs/api/samv3.html

@@ -1390,6 +1390,12 @@ as appropriate. Support for the ID parameter may be added in a future release.
 Version 3.3 was introduced in I2P release 0.9.25.
 </i></p>
 
+<p><i>
+In an earlier version of this specification, PRIMARY sessions were known as
+MASTER sessions. In both <code>i2pd</code> and <code>I2P+</code>, they are still
+known only as MASTER sessions.
+</i></p>
+
 <p>
 SAM v3.3 adds support for running streaming, datagrams, and raw subsessions on the same
 primary session, and for running multiple subsessions of the same style.