vagrant: Add Fedora 36 support.

- Add documentation for the vagrant setup on Fedora.
- Fix the container setup by adding the `z` option to the bind mounts so
that the selinux context allows sharing. This is according to the official
docker documentation:
https://docs.docker.com/storage/bind-mounts/#configure-the-selinux-label
https://www.vagrantup.com/docs/providers/docker/basics (section "Volume
Consistency")

Vagrantfile

@@ -18,7 +18,7 @@ Vagrant.configure("2") do |config|
   config.vm.box = "bento/ubuntu-20.04"
 
   config.vm.synced_folder ".", "/vagrant", disabled: true
-  config.vm.synced_folder ".", "/srv/zulip"
+  config.vm.synced_folder ".", "/srv/zulip", docker_consistency: "z"
 
   vagrant_config_file = ENV["HOME"] + "/.zulip-vagrant-config"
   if File.file?(vagrant_config_file)