Prepare and release 0.7.0

[chalin]

For known issues with Docsy 0.7.0, see:

• Prepare and release Docsy 0.7.1 docsy#1568

Tasks

• Mention known issues with Docsy 0.7.0 in the release comment, and link to the issue given above
• Drop warning at the start of the README (Drop warning at the start of the README (#222) #224)
• Docsy user guide: Add to the clone command --depth 1 --branch v0.7.0, so that version v.7.0 is cloned (see corresponding pull request).

[chalin]

@geriom - might you be available to submit a PR for this in case @deining isn't available?

[deining]

All three tasks are completed, closing this issue.

[chalin]

Great thanks!