Persist the ccache cache

- Similarly, ccache is needed to speed up C++ compilations (i.e. libreoffice)
diff --git a/modules/ccache.nix b/modules/ccache.nix
new file mode 100644
index 0000000..664a2a9
--- /dev/null
+++ b/modules/ccache.nix
@@ -0,0 +1,12 @@
+{
+  username,
+  config,
+  ...
+}: {
+  config.environment.persistence."/nix/persist".users.${username}.directories = [
+    {
+      directory = ".cache/ccache";
+      mode = "0700";
+    }
+  ];
+}