update README with intro and internals

README.md

@@ -1,5 +1,9 @@
 # Simple DIY VPN
 
+Tool to setup SOCKS proxy using ssh dynamic forward to your own server.
+Technically this is it not a VPN but practically achives the same thing for the
+most common use-case - browse websites without revealing your ip address
+
 ## Features
 
 * Starts automatically on demand and shuts down automatically when not used
@@ -7,7 +11,7 @@
 * Works on any VPS or home server with just ssh suppport.
   Distro/architecture/size does not matter. Only working ssh support required.
   No other software setup required on the server
-* Easy to setup multiple different VPNs to different server. No need to change
+* Easy to setup multiple different VPNs to different servers. No need to change
   whole system network settings.
 * Simple interactive cli utility to setup. No need to create/edit config files
 * Simple bash script with no dependencies - (ssh and systemd are usually
@@ -67,7 +71,12 @@ us1                  127.0.0.1:8070
 
 ## Internals
 
-TODO: Explain
+This sets up a systemd [user-generator][4]. The generator creates three units
+1. A [systemd-socket][5] that listens on the configured listen address.
+2. A socket activator unit that is triggered when someone connects to the
+   socket. This uses [systemd-socket-proxyd][6] to forward the request to the
+   ssh service and also setup idle timeout.
+3. The ssh service unit creates the ssh connection and setups dynamic forward.
 
 ## Future Ideas
 
@@ -79,3 +88,6 @@ TODO: Explain
 [1]: https://github.com/bekh6ex/firefox-container-proxy
 [2]: https://librewolf.net/
 [3]: https://wiki.archlinux.org/index.php?title=SSH_keys#Copying_the_public_key_to_the_remote_server
+[4]: https://man.archlinux.org/man/systemd.generator.7
+[5]: https://man.archlinux.org/man/systemd.socket.5.en
+[6]: https://man.archlinux.org/man/core/systemd/systemd-socket-proxyd.8.en