Update readme

Add setup instructions for first time contributors.
Fixes some order dependent failures in test suite.

Introduced in pull request #72.
Fixes test failures reported in #80.

You might want to merge this. It should work everywhere unless the user running
the tests has an insanely large cwd. I think it's better than the hack I linked
in issue #80.
Merge pull request #81 from deivid-rodriguez/fix_autolist_and_autoeval_tests

Fixes some order dependent failures in test suite.
Merge pull request #82 from deivid-rodriguez/fix_width_issues_in_test_suite

Fixes test failures reported in #80.
Merge remote-tracking branch 'upstream/master'
Add a simple test for rdebug command line behavior
Fix broken test dependency
Change Rakefile to run tests in subfolders of test/

A passing test file was previously being neglected
Add a test for rdebug --require