Add 25th NetBSD birthday news entry.

Index: index.xml
===================================================================
RCS file: /cvsroot/htdocs/changes/index.xml,v
retrieving revision 1.359
diff -u -p -r1.359 index.xml
--- index.xml	19 Mar 2018 04:32:38 -0000	1.359
+++ index.xml	21 Mar 2018 18:50:51 -0000
@@ -114,6 +114,48 @@
   <sect2 id="201803">
     <title>March 2018</title>
 
+    <sect3 id="netbsd-25th-birthday">
+      <title>21 Mar 2018 - NetBSD is 25 years old today</title>
+      <para>
+      A <code>"cvs log"</code> on many files in the NetBSD source tree shows:
+      </para>
+
+<screen>
+----------------------------
+revision 1.1
+date: 1993-03-21 10:45:37 +0100;  author: cgd;  state: Exp;
+branches:  1.1.1;
+Initial revision
+----------------------------
+</screen>
+
+      <para>
+      and, hard to believe, this is 25 years ago already!
+      </para>
+
+      <para>
+      We are still using cvs (but likely will not do that any more on our next
+      birthday), but lots of other things have changed. The number of architectures
+      has exploded, and so has the amount of third party software buildable on
+      NetBSD.
+      </para>
+
+      <para>
+      We are still a small project compared to other operating systems,
+      but like to think of our crowd as the most friendly, welcoming and
+      helpful one.
+      </para>
+
+      <para>
+      There is still a lot to do, and room for improvements --
+      keep up the good work and happy birthday, NetBSD!
+      </para>
+
+      <para>
+      <html:img src='../images/25yearsNetBSD.png'/>
+      </para>
+    </sect3>
+
     <sect3 id="netbsd712">
       <title>15 Mar 2018 - NetBSD 7.1.2 released</title>
       <para>NetBSD 7.1.2 is now available! Please see the <ulink