[landing] decrease spacing between paragraphs in landing page info blocks

Summary: @ashoat brought this up IRL, this diff addresses decreasing the spacing between paragraphs from 40px => 24px.

Test Plan:
Please see screenshots below

Before:

After:

Reviewers: ashoat, atul

Reviewed By: ashoat

Subscribers: tomek, ashoat

Differential Revision: https://phab.comm.dev/D8822