http2: updated README after NSS addition

Changed the support to a little matrix and added brief explanation of
what ALPN and NPN are for.

diff --git a/lib/README.http2 b/lib/README.http2
index eaa02fa..daa6338 100644 (file)
--- a/lib/README.http2
+++ b/lib/README.http2
@@ -31,11 +31,20 @@ HTTP2 with libcurl
   option that will cause libcurl to fail if not possible to use http2.
   Consider options to explicitly disable ALPN and/or NPN.
 
+  ALPN is the TLS extension that http2 is expected to use. The NPN extension
+  is for a similar purpose, was made prior to ALPN and is used for SPDY so
+  early http2 servers are implemented using NPN before ALPN support is
+  widespread.
+
 SSL libs
 
-  The challange is the ALPN and NPN support and all our different SSL
-  backends.  Right now we support ALPN and NPN with OpenSSL and ALPN with
-  GnuTLS.
+  The challenge is the ALPN and NPN support and all our different SSL
+  backends. You may need a fairly updated SSL library version for it to
+  provide the necessary TLS features. Right now we support:
+
+    OpenSSL: ALPN and NPN
+    NSS:     ALPN and NPN
+    GnuTLS:  ALPN
 
 Applications