Revise the style of a paragraph in README.md.

Revise the style of a paragraph in README.md.

Presently, one of the lines in README.md has trailing whitespace,
which was added by commit 363eb05996 to maintain a line break that
was in the non-Markdown version.  Instead of changing
.gitattributes, let's match this paragraph's style with the style
of the following paragraph, thereby removing the trailing
whitespace.

Reported-by: Peter Eisentraut
Reviewed-by: Daniel Gustafsson
Discussion: https://postgr.es/m/c0a4e906-c6fe-4519-bd15-28dfcd03fdb2%40eisentraut.org