Update README.md

Signed-off-by: Teddysun <[email protected]>

docker/l2tp/README.md

@@ -2,9 +2,9 @@
 
 Docker image to run a L2TP/IPsec VPN Server, with both `L2TP/IPsec PSK` and `IPSec Xauth PSK`.
 
-Based on Debian 9 (Stretch) with libreswan-3.27 (IPsec VPN software) and xl2tpd-1.3.12 (L2TP daemon).
+1. Based on Debian 9 (Stretch) with [libreswan-3.27 (IPsec VPN software)](https://github.com/libreswan/libreswan) and [xl2tpd-1.3.12 (L2TP daemon)](https://github.com/xelerance/xl2tpd).
 
-Based on alpine with libreswan-3.21 (IPsec VPN software) and xl2tpd-1.3.10 (L2TP daemon).
+2. Based on alpine with [libreswan-3.21 (IPsec VPN software)](https://pkgs.alpinelinux.org/package/v3.8/community/x86_64/libreswan) and [xl2tpd-1.3.10 (L2TP daemon)](https://pkgs.alpinelinux.org/package/v3.8/main/x86_64/xl2tpd).
 
 Docker images are built for quick deployment in various computing cloud providers.