Make utility to run server in dev mode (#219)

Often when I'm building, I'll do the following:

```
make generate
make build
./build/kolide.exe serve --dev
```

It would be nicer if I could just use make to run the dev server instead
of having to type out the full path every time:

```
make generate
make build
make run
```

Makefile

@@ -55,6 +55,8 @@ define HELP_TEXT
 	make lint-go      - Run the Go linters
 	make lint-js      - Run the JavaScript linters
 
+	make run          - Run the Kolide server in dev mode
+
 endef
 
 help:
@@ -124,6 +126,9 @@ else
 	rm -f assets/bundle.js
 endif
 
+run:
+	$(OUTPUT) serve --dev
+
 docker-build-circle:
 	@echo ">> building docker image"
 	docker build -t "${DOCKER_IMAGE_NAME}:${DOCKER_IMAGE_TAG}" .

README.md

@@ -288,4 +288,11 @@ This will use in-memory mocks for the database, print emails to the console,
 etc. If you're demo-ing Kolide or testing a quick feature, dev mode is ideal.
 Keep in mind that, since everything is in-memory, when you kill the process,
 everything you did in dev mode will be lost. This is nice for development but
-not so nice for production environments.
+not so nice for production environments.
+
+If you've used `make build` to build the Kolide binary, you can also run the
+following to launch an in-memory instance of the server:
+
+```
+make run
+```