Help: Increase font size in Happiness Engineer text

[dllh]

The font size is a little small at narrower widths, and this makes it a little friendlier to read at smaller screen sizes.

Repro:

1. Visit http://calypso.localhost:3000/help/
2. Observe the list of Happiness Engineers at the bottom
3. Reduce screen size to a width narrower than 660px.
4. Observe the font size of the text underneath "We care about your happiness"

This would fix #1390. Before the fix:

With the fix:

[dllh]

Cc @mattmiklic @omarjackman

[omarjackman]

👍 This looks good to me

[mattmiklic]

Looks good 👍 11px is too small for paragraph text; that was my mistake in the initial mockup.