Update the README to include a tip for reducing Docker image sizes

[trajano]

For CI environments that build Docker images from Maven configure a profile like this so that it will download the noarch libraries and just the Linux image.

		<profile>
			<id>unix</id>
			<activation>
				<os>
					<family>unix</family>
					<name>Linux</name>
				</os>
			</activation>
			<dependencies>
				<dependency>
					<groupId>io.humble</groupId>
					<artifactId>humble-video-noarch</artifactId>
					<version>0.3.0</version>
				</dependency>
				<dependency>
					<groupId>io.humble</groupId>
					<artifactId>humble-video-arch-x86_64-pc-linux-gnu6-debug</artifactId>
					<version>0.3.0</version>
  				</dependency>
			</dependencies>
		</profile>