README: Add libssl to prerequisites.

diff --git a/README b/README
index a681916c3cbcc0cdf141de7664f1a5f5d8262e1e..7e493db39ec92d894938d87c1ea930a25f58c737 100644 (file)
--- a/README
+++ b/README
@@ -103,6 +103,12 @@ Prerequisites
 
     <https://oss.oetiker.ch/rrdtool/>
 
+  * libssl:
+    The Secure Sockets Layer toolkit library is used to encrypt and
+    authenticate TCP connections.
+
+    <http://openssl.org/>
+
 Testing
 -------