[all pages - Understanding & Techniques] link the first text to index page

[shawna-slh]

• [ ] add link to the Understanding index page in:

<div class="minimal-header-name">WCAG 2.2 Understanding Docs</div>

• [ ] add link to the Techniques index page in:

<div class="minimal-header-name">WCAG 2.2 Techniques</div>

[shawna-slh]

duplicate