add link to blogpost to clarify what backends are

diff --git a/docs/markdown/appendix/backend-writers-guide.md b/docs/markdown/appendix/backend-writers-guide.md
index c8254ad8bf914840a235422168deb03f476ea032..e3e186e16e327b8314df9873a8a7fd1e1e134dbe 100644 (file)
--- a/docs/markdown/appendix/backend-writers-guide.md
+++ b/docs/markdown/appendix/backend-writers-guide.md
@@ -1,5 +1,11 @@
 # Backend writers' guide
-PDNS backends are implemented via a simple yet powerful C++ interface. If your needs are not met by the PipeBackend, you may want to write your own. Before doing any PowerDNS development, please visit [the wiki](http://wiki.powerdns.com).
+
+PowerDNS backends are implemented via a simple yet powerful C++ interface. 
+If your needs are not met by the PipeBackend, you may want to write your
+own.  Before doing any PowerDNS development, please visit [the
+wiki](http://wiki.powerdns.com).  Also please read [this blog
+post](http://blog.powerdns.com/2015/06/23/what-is-a-powerdns-backend-and-how-do-i-make-it-send-an-nxdomain/)
+which has a FAQ and several pictures that help explain what a backend is.
 
 A backend contains zero DNS logic. It need not look for CNAMEs, it need not return NS records unless explicitly asked for, etcetera. All DNS logic is contained within PDNS itself - backends should simply return records matching the description asked for.