Add Ubuntu install instructions

[s-makin]

Add snap install instructions to the documentation, with a link to the woke
snap in the snap store.

Please check if the PR fulfills these requirements

• [Y] The commit message follows our guidelines
• [Y] Tests for the changes have been added (for bug fixes / features)
• [Y] Docs have been added / updated (for bug fixes / features) see docs/README.md

What kind of change does this PR introduce? (Bug fix, feature, docs update, ...)
docs update

What is the current behavior? (You can also link to an open issue here)
N/A

What is the new behavior (if this is a feature change)?
N/A

Does this PR introduce a breaking change? (What changes might users need to make due to this PR?)
No, it only touches the docs

Other information:

[github-actions]

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