feat(languages/x509): add x509-mode

This allows using M-x x509-dwim to decode any PEM encoded OpenSSL
certs/keys and display all details via OpenSSL.

modules/languages/siren-x509.el

@@ -0,0 +1,13 @@
+;;; siren-x509.el --- jimeh's Emacs Siren: x509-mode configuration.
+
+;;; Commentary:
+
+;; Basic configuration for x509-mode.
+
+;;; Code:
+
+(use-package x509-mode
+  :defer t)
+
+(provide 'siren-x509)
+;;; siren-x509.el ends here