Add current docs link to README

[seabbs]

Description

In #563 @sbfnk introduced new functionality to post users at the alternative version of the docs to the one they are currently viewing. However, if they are not on the HTML docs then there is currently no link to the current version of the HTML docs that they are looking at. It could be nice if this were the case.

This PR adds this. I think worth some discussion to check it makes sense .

Checklist

• My PR is based on a package issue and I have explicitly linked it.
• I have included the target issue or issues in the PR title as follows: issue-number: PR title
• I have tested my changes locally.
• I have added or updated unit tests where necessary.
• I have updated the documentation if required.
• I have built the package locally and run rebuilt docs using roxygen2.
• My code follows the established coding standards and I have run lintr::lint_package() to check for style issues introduced by my changes.
• I have added a news item linked to this PR.
• I have reviewed CI checks for this PR and addressed them as far as I am able.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (61905cf) 85.15% compared to head (121331d) 85.15%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #582   +/-   ##
=======================================
  Coverage   85.15%   85.15%           
=======================================
  Files          21       21           
  Lines        1711     1711           
=======================================
  Hits         1457     1457           
  Misses        254      254           

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[nikosbosse]

Good idea, I like this. Thank you!