tagging issue

[DavidCozens]

First of all thanks for putting up these containers - really helpful - it makes getting started really easy. However I hit a problem that may get others, when I ran the example commands from the readme I saw the error message Error response from daemon: manifest unknown
On investigation I found that there is no latest tag, I switched to using cppcheck:2.6 rather than cppcheck:latest and everything worked.
It would help others I think if the example commands were updated