layout: align read more buttons
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.