website: add mailinglist archive information

This patch adds mailinglist archive information. This is a general information and several people asking if there is any mailinglist archive.

---
 website/index.txt | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

index 0a135e2..2dfa962 100644
@@ -1,6 +1,9 @@
 linux-wpan
 ==========
-Mailinglist <[email protected]>
+Mailinglist
+
+<[email protected]>
+http://www.spinics.net/lists/linux-wpan[Mailinglist-Archive]
 
 .IRC
 #linux-wpan on irc.freenode.net

2.3.5