docs: add proxy documentation

docs/reference/providers/docker.md

@@ -35,7 +35,7 @@ Where `ENVIRONMENT` will be one of `production`, `staging`.
 
 ## Exposing services
 
-Once a valid compose file has been found, **seelf** will apply some **heuristics** to determine which services should be exposed and where.
+Once a valid compose file has been found and **only if** the target [manages the proxy itself](/reference/targets#proxy), **seelf** will apply some **heuristics** to determine which services should be exposed and where.
 
 It will consider any service with **port mappings** to be exposed.
 

docs/reference/targets.md

@@ -6,9 +6,16 @@ Targets represents an **host** where your deployments will be exposed. When conf
 For now, only one target per host is allowed.
 :::
 
-## Url
+## Proxy configuration {#proxy}
 
-The url **determine where your applications will be made available**. It should be a **root url** as applications will use subdomains on it.
+When declaring a target, you must choose how the proxy (needed to make your services available from the outside world) should be managed:
+
+- **Automatic**: **seelf** will deploy and configure a [traefik](https://traefik.io/traefik/) proxy on the target. Services urls will be automatically generated based on the [target's url](#url) and [service file](/reference/providers/docker#exposing-services) when deploying. Exposed services will also join the proxy network.
+- **Manual**: you're in charge of **everything** related to services exposure. **seelf** will deploy services on this target without attempting to expose them in any way.
+
+### Url
+
+If the target manages the proxy itself, this url **determines where your applications will be made available**. It should be a **root url** as applications will use subdomains on it.
 
 The scheme associated with this url (`http` or `https`) will determine if certificates should be generated or not.