Closes #49 Documentation: Updated "Get Started" page

[nissinbo]

Closes #49
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[AndersAskeland]

Thanks for the pull request @nissinbo ! 👍

See my comments below. In addition, I think it would be great to add a "Derivations" section, where we quickly mention the ratio functions we have. See https://pharmaverse.github.io/admiralophtha/articles/admiralophtha.html for an example.

[AndersAskeland]

I think we should change to one code chunk and add some text about adding issues on the github repository.

Besides that, it looks good to merge 👍

[AndersAskeland]

LGTM! Thank you for the work on this @nissinbo 👍