Reorder installation section of README

[4-20ma]

Description

This makes documentation flow more naturally.

Issues Resolved

Resolves #73.

Check List

General

• Code follows coding style defined in STYLE.md
• Doxygen comments are included inline with code
• No unnecessary whitespace; check with git diff --check before committing.

The following have been modified to reflect new features, if warranted

• README.md
• keywords.txt (use tabs as whitespace separators)
• library.properties
• examples/ - update or create new ones, as warranted

The following have NOT been modified

• doc/ - will be updated upon versioned release
• .ruby-gemset
• .ruby-version
• CHANGELOG.md - will be updated upon versioned release (HISTORY.md is deprecated)
• Gemfile
• LICENSE
• VERSION - will be updated upon versioned release