Updating Compose documentation

- Split out commands into individual pages for maintainability
- Add full usage in commands pages for usability
- Updated description of the run command
- adding in Aanand's comment

Signed-off-by: Mary Anthony <mary@docker.com>

docs/reference/pull.md

@@ -0,0 +1,20 @@
+<!--[metadata]>
++++
+title = "pull"
+description = "Pulls service images."
+keywords = ["fig, composition, compose, docker, orchestration, cli,  pull"]
+[menu.main]
+parent = "smn_compose_cli"
++++
+<![end-metadata]-->
+
+# pull
+
+```
+Usage: pull [options] [SERVICE...]
+
+Options:
+--allow-insecure-ssl    Allow insecure connections to the docker registry
+```
+
+Pulls service images.