Update docs

- Improve IKEv2 docs. The strongSwan Android VPN client requires
  an "IP address" in the VPN server certificate's subjectAltName field
  in addition to "DNS name", when connecting using the server's IP.
  The certutil commands have been updated to add this field.
- Other improvements to docs

docs/uninstall.md

@@ -15,7 +15,7 @@ Follow these steps to remove the VPN. Commands must be run as `root`, or with `s
 
 ## First step
 
-```
+```bash
 service ipsec stop
 service xl2tpd stop
 rm -rf /usr/local/sbin/ipsec /usr/local/libexec/ipsec
@@ -69,7 +69,7 @@ Remove these config files:
 
 Copy and paste for fast removal:
 
-```
+```bash
 rm -f /etc/ipsec.conf* /etc/ipsec.secrets* /etc/ppp/chap-secrets* /etc/ppp/options.xl2tpd* \
       /etc/pam.d/pluto /etc/sysconfig/pluto /etc/default/pluto
 rm -rf /etc/ipsec.d /etc/xl2tpd