small change on jbigi.html, note on GMP4.2.2

www.i2p2/pages/jbigi.html

@@ -16,7 +16,8 @@ included in your OS / distribution or installed already, it can be received from
 <a href="http://www.swox.com/gmp/">http://www.swox.com/gmp/</a>. Even if you
 have already installed it as binary, it might still be worth a try to compile
 GMP yourself, since then it will be able to use the specific instructions of
-your processor.</p>
+your processor. For I2P source of 0.6.1.31-6 latest GMP 4.2.2 is needed by
+buildscript</p>
 
 <h2>Step-by-step instructions</h2>
 <ol>
@@ -51,4 +52,4 @@ should be a lot faster.</li>
 </ol>
 
 <p>Feedback is appreciated</p>
-{% endblock %}
+{% endblock %}