Added comments documenting how to export SSL keys from .pfx

conf/app.ini

@@ -22,6 +22,11 @@ DISABLE_ROUTER_LOG = false
 ; Generate steps:
 ; $ cd path/to/gogs/custom/https
 ; $ ./gogs cert -ca=true -duration=8760h0m0s -host=myhost.example.com
+;
+; Or from a .pfx file exported from the Windows certificate store (do
+; not forget to export the private key):
+; $ openssl pkcs12 -in cert.pfx -out cert.pem -nokeys
+; $ openssl pkcs12 -in cert.pfx -out key.pem -nocerts -nodes
 CERT_FILE = custom/https/cert.pem
 KEY_FILE = custom/https/key.pem
 ; Upper level of template and static file path