Add testing instructions + slight sshconf mod

.ssh/config

@@ -1,4 +1,5 @@
 Host code.kpuig.net
+    HostName code.kpuig.net
     Port 4222
     User git
     IdentityFile <PATH-TO-YOUR-KEYFILE>

README.md

@@ -9,3 +9,9 @@
 4. Go into your Gitea Settings, then SSH/GPG Keys section, then upload your public key (in most cases, a file called `id_ed25519.pub`).
 
 5. You can now contribute code!
+
+## Test connection
+
+`ssh code.kpuig.net`
+
+If this command gives you anything but an affirmative that you're configured correctly, that means you have misconfigured something, most likely in SSH but possibly in git.