Merged: Fix typo

Merge commit 'refs/pull/9/head' of https://github.com/apache/incubator-freemarker-site
diff --git a/src/main/docgen/book.xml b/src/main/docgen/book.xml
index c624e48..366e34f 100644
--- a/src/main/docgen/book.xml
+++ b/src/main/docgen/book.xml
@@ -1234,7 +1234,7 @@
       <section xml:id="how-to-contribute">
         <title>How do I contribute?</title>
 
-        <para>First you should <link linkend="mailing-lists">subsrcribe to the
+        <para>First you should <link linkend="mailing-lists">subscribe to the
         developer mailing list</link> to discuss what you plan to do.</para>
 
         <para>Then, fork the project on Github, and start working on the