openfortivpn: add page (#4902)

pages/linux/openfortivpn.md

@@ -0,0 +1,20 @@
+# openfortivpn
+
+> A VPN client, for Fortinet's proprietary PPP+SSL VPN solution.
+> More information: <https://github.com/adrienverge/openfortivpn>.
+
+- Connect to a VPN with a username and password:
+
+`openfortivpn --username={{username}} --password={{password}}`
+
+- Connect to a VPN using a specific configuration file (defaults to `/etc/openfortivpn/config`):
+
+`sudo openfortivpn --config={{path/to/config}}`
+
+- Connect to a VPN by specifiying the host and port:
+
+`openfortivpn {{host}}:{{port}}`
+
+- Trust a given gateway by passing in its certificate's sha256 sum:
+
+`openfortivpn --trusted-cert={{sha256_sum}}`