Manually specify "C-c p" as projectile prefix key

Projectile no longer sets up it's prefix key automatically, so this has
to be manually done now.

modules/projects/siren-projectile.el

@@ -14,6 +14,8 @@
   ("C-x C-t" . projectile-find-file)
   ("C-x t" . projectile-find-test-file)
   ("C-x C-v" . projectile-switch-to-buffer)
+  (:map projectile-mode-map
+        ("C-c p" . projectile-command-map))
 
   :init
   (setq projectile-cache-file (expand-file-name