Update installation docs to include Docker, others

As per this comment
https://gitlab.com/gitlab-com/support/issues/374#note_22056587 we're
moving documentation around from the support workflows.

doc/install/README.md

@@ -4,3 +4,6 @@
 - [Requirements](requirements.md)
 - [Structure](structure.md)
 - [Database MySQL](database_mysql.md)
+- [Digital Ocean and Docker](digitaloceandocker.md)
+- [Docker](https://gitlab.com/gitlab-org/gitlab-ce/tree/master/docker)
+- [All installation methods](https://about.gitlab.com/installation/)

doc/install/digitaloceandocker.md

+# Digital Ocean and Docker
+
+## Initial setup
+
+In this guide you'll configure a Digital Ocean droplet and set up Docker
+locally on either macOS or Linux.
+
+### On macOS
+
+#### Install Docker Toolbox
+
+1. [https://www.docker.com/products/docker-toolbox](https://www.docker.com/products/docker-toolbox)
+
+### On Linux
+
+#### Install Docker Engine
+
+1. [https://docs.docker.com/engine/installation/linux](https://docs.docker.com/engine/installation/linux/)
+
+#### Install Docker Machine
+
+1. [https://docs.docker.com/machine/install-machine](https://docs.docker.com/machine/install-machine/)
+
+_The rest of the steps are identical for macOS and Linux_
+
+### Create new docker host
+
+1. Login to Digital Ocean
+1. Generate a new API token at https://cloud.digitalocean.com/settings/api/tokens
+
+
+This command will create a new DO droplet called `gitlab-test-env-do` that will act as a docker host.
+
+**Note: 4GB is the minimum requirement for a Docker host that will run more then one GitLab instance**
+
++ RAM: 4GB
++ Name: `gitlab-test-env-do`
++ Driver: `digitalocean`
+
+
+**Set the DO token** - Replace the string below with your generated token
+
+```
+export DOTOKEN=cf3dfd0662933203005c4a73396214b7879d70aabc6352573fe178d340a80248
+```
+
+**Create the machine**
+
+```
+docker-machine create \
+  --driver digitalocean \
+  --digitalocean-access-token=$DOTOKEN \
+  --digitalocean-size "4gb" \
+    gitlab-test-env-do
+```
+
++ Resource: https://docs.docker.com/machine/drivers/digital-ocean/
+
+
+### Creating GitLab test instance
+
+
+#### Connect your shell to the new machine
+
+
+In this example we'll create a GitLab EE 8.10.8 instance.
+
+
+First connect the docker client to the docker host you created previously.
+
+```
+eval "$(docker-machine env gitlab-test-env-do)"
+```
+
+You can add this to your `~/.bash_profile` file to ensure the `docker` client uses the `gitlab-test-env-do` docker host
+
+
+#### Create new GitLab container
+
++ HTTP port: `8888`
++ SSH port: `2222`
+   + Set `gitlab_shell_ssh_port` using `--env GITLAB_OMNIBUS_CONFIG `
++ Hostname: IP of docker host
++ Container name: `gitlab-test-8.10`
++ GitLab version: **EE** `8.10.8-ee.0`
+
+#####  Setup container settings
+
+```
+export SSH_PORT=2222
+export HTTP_PORT=8888
+export VERSION=8.10.8-ee.0
+export NAME=gitlab-test-8.10
+```
+
+#####  Create container
+```
+docker run --detach \
+--env GITLAB_OMNIBUS_CONFIG="external_url 'http://$(docker-machine ip gitlab-test-env-do):$HTTP_PORT'; gitlab_rails['gitlab_shell_ssh_port'] = $SSH_PORT;" \
+--hostname $(docker-machine ip gitlab-test-env-do) \
+-p $HTTP_PORT:$HTTP_PORT -p $SSH_PORT:22 \
+--name $NAME \
+gitlab/gitlab-ee:$VERSION
+```
+
+#### Connect to the GitLab container
+
+##### Retrieve the docker host IP
+
+```
+docker-machine ip gitlab-test-env-do
+# example output: 192.168.151.134
+```
+
+
++ Browse to: http://192.168.151.134:8888/
+
+
+##### Execute interactive shell/edit configuration
+
+
+```
+docker exec -it $NAME /bin/bash
+```
+
+```
+# example commands
+root@192:/# vi /etc/gitlab/gitlab.rb
+root@192:/# gitlab-ctl reconfigure
+```
+
+#### Resources
+
++ [https://docs.gitlab.com/omnibus/docker/](https://docs.gitlab.com/omnibus/docker/)
++ [https://docs.docker.com/machine/get-started/](https://docs.docker.com/machine/get-started/)
++ [https://docs.docker.com/machine/reference/ip/](https://docs.docker.com/machine/reference/ip/)+