Make smooth animation for intro

Intro should be split into two parts: doublet and triplet.
Each animation should be made smooth using SVG animation.
Something like [vivus](https://maxwellito.github.io/vivus/) can be used with existing [SVG frames](https://github.com/linksplatform/Documentation/tree/master/doc/Intro).

Start with the existing SVG frames in doc/Intro and review the Vivus example linked in the issue. Determine how the intro should be split into doublet and triplet sections, then make both animations smooth with SVG animation. Done means the intro contains the two parts and each has a smooth animation using the existing frames.

Written by the indexing model from the issue text.