Update HTTP API docs (#827)

docs/http-api-mode.md

@@ -4,7 +4,7 @@ Watchtower provides an HTTP API mode that enables an HTTP endpoint that can be r
 
 ---
 
-To enable this mode, use the flag `--http-api`. For example, in a Docker Compose config file:
+To enable this mode, use the flag `--http-api-update`. For example, in a Docker Compose config file:
 
 ```yaml
 version: '3'
@@ -19,7 +19,7 @@ services:
     image: containrrr/watchtower
     volumes:
       - /var/run/docker.sock:/var/run/docker.sock
-    command: --debug --http-api
+    command: --debug --http-api-update
     environment:
       - WATCHTOWER_HTTP_API_TOKEN=mytoken
     labels:
@@ -31,5 +31,5 @@ services:
 Notice that there is an environment variable named WATCHTOWER_HTTP_API_TOKEN. To prevent external services from accidentally triggering image updates, all of the requests have to contain a "Token" field, valued as the token defined in WATCHTOWER_HTTP_API_TOKEN, in their headers. In this case, there is a port bind to the host machine, allowing to request localhost:8080 to reach Watchtower. The following `curl` command would trigger an image update:
 
 ```bash
-curl -H "Token: mytoken" localhost:8080/v1/update
-```
+curl -H "Authorization: Bearer mytoken" localhost:8080/v1/update
+```