OPEN: Minor CI and Readme Improvements

[Victor-Jung]

In this PR, we:

• Improves the README, explaining how to get started with Deeploy using the Docker container. In the future I will add more content such as 'How to install dependencies manually', 'How to add tests to the CI', and 'How to add new dependencies'.
• Update the link of the docker container used to run the CI; previously, it was pointing at my fork.
• BUGFIX: Add a step to retry on timeout for the tests of large networks on Siracusa.
• Schedule a CI run every 6 days at 2am to keep the cache fresh.

[Xeratec]

LGTM.
Do you want to add a section explaining the CI in the Readme in this PR or another one? As this PR is not a critical change I suggest adding it here. Otherwise feel free to merge.

[Victor-Jung]

@Xeratec I improved the README and added a read Getting Started section for beginners. More detailed tutorials on the CI and CD flow will come later if that's fine for you.

[Xeratec]

LGTM, feel free to merge.
One question, tough. Do we have more insight into why some test on Siracusa time out sometimes? If it is a problem in our codebase, please open an issue.