Suggestion for installation instructions

[dmarcoux]

sobelow is often running in continuous integration pipelines and when it does, it will more often than not be in the test environment. On top of this, sobelow doesn't have to be started as a runtime application, so runtime: false should also be added to the installation instructions. This is what I suggest for the README:

def deps do
  [
    {:sobelow, "~> 0.11", only: [:dev, :test], runtime: false}
  ]
end

I am happy to send a PR if you agree with the suggestion.

[houllette]

Great suggestion, @dmarcoux - I would happily welcome a PR if you made one!