Update CONTRIBUTING.md

Add details of README.md to description of submodule.

Add details of how to generate README.md to section on
how to implement new exercise.

markdown: add to track

Nix public access

Ignore build.gradle when CI runs tests against changeset

* make classes and methods package private #1052

* method accessor changes

This reverts commit 58ed692a57b235d3ab3f8bb68e9375287eff8e47.

This reverts commit b14f3aef3d60abc5964b0224b3ddbd006e66d95d.

removing public access modifier from IsogramChecker class and methods

Fixes #1055 

* make classes and methods package private #1055

* changed nested class to public

* made Element<T> private and its constructor package-private

grade-school: make classes and methods package private in reference solution

trying something else

* Temporary commit to test journey test fix

* Fix journey test

Make sure run-journey-test-from-ci doesn't try to run settings.gradle as
an exercise.

* Revert "Temporary commit to test journey test fix"

This reverts commit eb0d5dd091d8f3c633fcda7742312a2c261bff8b.

maintainers.json: add @sjwarner-bp

etl: remove public access modifier from etl

clock: make classes and methods package private in reference solution

accumulate: make classes and methods package private in reference solution

binary: make classes and methods package private in reference solution

reverse-string: change unlocked_by exercise to two-fer

fix broken links in maintaining.md

reverse-string: add to track

circular-buffer: make classes and methods package private in reference solution