Slapos testing docs

Update docs to describe how to run test locally

/reviewed-on !705
3 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.SlapRunner.ResilienceTest-Master

00:24:46

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

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failed SlapOS.SoftwareReleases.IntegrationTest-Master

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