Add a docker-compose & let's encrypt user-guide

docs/content/user-guides/docker-compose/basic-example/index.md

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+# Docker-compose basic example
+
+In this section we quickly go over a basic docker-compose file exposing a simple service using the docker provider.  
+This will also be used as a starting point for the the other docker-compose guides.  
+
+## Setup
+
+- Edit a `docker-compose.yml` file with the following content:
+
+```yaml
+--8<-- "content/user-guides/docker-compose/basic-example/docker-compose.yml"
+```
+
+- Replace `whoami.localhost` by your **own domain** within the `traefik.http.routers.whoami.rule` label of the `whoami` service.
+- Run `docker-compose up -d` within the folder where you created the previous file.
+- Wait a bit and visit `http://your_own_domain` to confirm everything went fine.
+	You should see the output of the whoami service. Something similar to:
+	
+	```text
+	Hostname: d7f919e54651
+	IP: 127.0.0.1
+	IP: 192.168.64.2
+	GET / HTTP/1.1
+	Host: whoami.localhost
+	User-Agent: curl/7.52.1
+	Accept: */*
+	Accept-Encoding: gzip
+	X-Forwarded-For: 192.168.64.1
+	X-Forwarded-Host: whoami.localhost
+	X-Forwarded-Port: 80
+	X-Forwarded-Proto: http
+	X-Forwarded-Server: 7f0c797dbc51
+	X-Real-Ip: 192.168.64.1
+	```
+
+## Details
+
+- As an example we use [whoami](https://github.com/containous/whoami) (a tiny Go server that prints os information and HTTP request to output) which was used to define our `simple-service` container.
+
+- We define an entry point, along with the exposure of the matching port within docker-compose, which basically allow us to "open and accept" HTTP traffic: 
+
+```yaml
+command:
+  # Traefik will listen to incoming request on the port 80 (HTTP)
+  - "--entrypoints.web.address=:80"
+
+ports:
+  - "80:80"
+```
+
+- We expose the Traefik API to be able to check the configuration if needed:
+
+```yaml
+command:
+  # Traefik will listen on port 8080 by default for API request.
+  - "--api=true"
+
+ports:
+  - "8080:8080"
+```
+
+!!! Note
+
+    If you are working on a remote server, you can use the following command to display configuration (require `curl` & `jq`): 
+     
+    ```bash
+    curl -s 127.0.0.1:8080/api/rawdata | jq .
+    ```
+
+- We allow Traefik to gather configuration from Docker:
+
+```yaml
+traefik:
+  command:
+    # Enabling docker provider
+    - "--providers.docker=true"
+    # Do not expose containers unless explicitly told so
+    - "--providers.docker.exposedbydefault=false"
+  volumes:
+    - "/var/run/docker.sock:/var/run/docker.sock:ro"
+
+whoami:
+  labels:
+    # Explicitly tell Traefik to expose this container
+    - "traefik.enable=true"
+    # The domain the service will respond to
+    - "traefik.http.routers.whoami.rule=Host(`whoami.localhost`)"
+    # Allow request only from the predefined entry point named "web"
+    - "traefik.http.routers.whoami.entrypoints=web"
+```