Remove installation section from README.md (#520)
Remove installation section from README.md (#520)

At this point, most Dart users are aware how to use pub packages, and
the recommended version constraint in our README.md is frequently
forgotten (at least by me) when bumping versions in the
pubspec/changelog.

Also moves first-level headings to underline form to make them easier to
read in text editors.
kevmoo/quiver-dart,kevmoo/quiver-dart,google/quiver-dart,cbracken/quiver-dart,cbracken/quiver-dart