feat: command to upgrade outline (#1727)

* Add upgrade script to package.json

* Update the docs to include docker and yarn guides

README.md

@@ -75,6 +75,20 @@ In development you can quickly get an environment running using Docker by follow
     1. Ensure that the bot token scope contains at least `users:read`
 1. Run `make up`. This will download dependencies, build and launch a development version of Outline
 
+### Upgrade
+
+#### Docker
+
+If you're running Outline with Docker you'll need to run migrations within the docker container after updating the image. The command will be something like:
+```
+docker run --rm outlinewiki/outline:latest yarn sequelize:migrate
+```
+#### Yarn
+
+If you're running Outline by cloning this repository, run the following command to upgrade:
+```
+yarn upgrade
+```
 
 ## Development