docs: mention reloading sshd

after changing the sshd config, it's necessary to reload ssh. added instructions on how to do this to the self-hosting guide

Signed-off-by: Samuel Newman <[e-mail]>

docs/knot-hosting.md

···
 EOF
 ```
 
+Then, reload `sshd`:
+
+```
+sudo systemctl reload ssh
+```
+
 Next, create the `git` user. We'll use the `git` user's home directory
 to store repositories: