The "Read more" buttons in the "Featured APIs" section used to be put at
some constant spacing after the description-text. This doesn't look very
nice when two APIs line up where the text differs enough in length to
cause the "Read more" buttons to not line up.

This uses the "display: flex" related utilities from Bootstrap to make
the "Read more" buttons align to the bottom of the div, which makes the
buttons line up. This leads to some reduction in visual noise when
skimming the page.