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/scale.md

@@ -0,0 +1,21 @@
+<!--[metadata]>
++++
+title = "scale"
+description = "Sets the number of containers to run for a service."
+keywords = ["fig, composition, compose, docker, orchestration, cli,  scale"]
+[menu.main]
+parent = "smn_compose_cli"
++++
+<![end-metadata]-->
+
+# scale
+
+```
+Usage: scale [SERVICE=NUM...]
+```
+
+Sets the number of containers to run for a service.
+
+Numbers are specified as arguments in the form `service=num`. For example:
+
+    $ docker-compose scale web=2 worker=3