server: Add a cache folder

Since Jellyfin filled /var/cache/Jellyfin/images nextcloud failed to
login.

/var/cache is limited to 30GiB of size

Author: RaHoni

README.md

@@ -0,0 +1,10 @@
+# Install
+
+## Server
+
+Limit the size of /tmp and /var/cache via 
+
+'''
+btrfs qgroup limit 30G /btrfs/tmp
+btrfs qgroup limit 30G /btrfs/cache
+'''

server/disko.nix

@@ -29,6 +29,9 @@ in
               type = "btrfs";
               extraArgs = [ "-f" ];
               subvolumes = {
+                "/" = {
+                  mountpoint = "/btrfs";
+                };
                 "/nix" = {
                   mountpoint = "/nix";
                   mountOptions = [
@@ -39,6 +42,9 @@ in
                 "/tmp" = {
                   mountpoint = "/tmp";
                 };
+                "/cache" = {
+                  mountpoint = "/var/cache";
+                };
                 "/permament" = {
                   mountpoint = "/permament";
                   mountOptions = [