docs(dokku): Add notes for updating an existing deployment

Author: sman591

docs/deployment-dokku.md

@@ -3,12 +3,36 @@ id: deployment-dokku
 title: Dokku Deployment
 ---
 
-Below are steps & notes to deploy HackathonManager on Dokku.
-
->This assumes you already have a virtual machine with [Dokku](http://dokku.viewdocs.io/dokku/) running on it, and can SSH into the VM. DNS should be set up as well, but isn't required for bare minimum functionality.
+>These docs assume you already have a virtual machine with [Dokku](http://dokku.viewdocs.io/dokku/) running on it, and can SSH into the VM. DNS should be set up as well, but isn't required for bare minimum functionality.
 >
 >If you need a VM, check out [DigitalOean](https://m.do.co/c/b5ee103e23c3) or [Linode](https://www.linode.com/?r=e90a6fb2a6999fb4ec7b60b1add3e288f97954bf) and the [Dokku docs](http://dokku.viewdocs.io/dokku/) to get started.
 
+## Updating an existing deployment
+
+If you already have a deployment of HackathonManager on Dokku, follow these steps to update it.
+
+* If you already have the hackathon-manager repo cloned locally:
+```bash
+# cd into the directory you have hackathon-manager cloned
+cd hackathon-manager
+git pull
+# Skip to "git push" if you already added the remote
+git remote add dokku dokku@your-host.example.com:hm
+git push dokku master
+```
+
+* If you don't have it cloned locally:
+```bash
+git clone git@github.com:codeRIT/hackathon-manager
+cd hackathon-manager
+git remote add dokku dokku@your-host.example.com:hm
+git push dokku master
+```
+
+## Setting up a new deployment
+
+Below are steps & notes to deploy HackathonManager on Dokku.
+
 If you have any questions at all, please don't hesitate to reach out to [Stuart](https://github.com/sman591)! This doc is very much a work in progress but we want to keep it as up to date as possible.
 
 ## Dokku plugins