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/build.md

@@ -0,0 +1,22 @@
+<!--[metadata]>
++++
+title = "build"
+description = "build"
+keywords = ["fig, composition, compose, docker, orchestration, cli,  build"]
+[menu.main]
+parent = "smn_compose_cli"
++++
+<![end-metadata]-->
+
+# build
+
+```
+Usage: build [options] [SERVICE...]
+
+Options:
+--no-cache  Do not use cache when building the image.
+```
+
+Services are built once and then tagged as `project_service`, e.g.,
+`composetest_db`. If you change a service's Dockerfile or the contents of its
+build directory, run `docker-compose build` to rebuild it.