tools: Add README entry for workflow scripts

Issue #28.
tools/workflow: Add skeleton implementation

Issue #28.
tools/workflow: Add get_git_toplevel()

Issue #28.
tools/workflow: Add missing comments

Issue #28.
tools/workflow: Implement fail_if_tree_not_clean()

Issue #28.
tools/workflow: Define some useful variables

Issue #28.
tools/workflow: Add empty fail_if_issue_not_valid()

Will need to setup a command line GitHub issue tracker interface to
complete work on this.

Issue #28.
tools/workflow: Complete implementation of new()
tools/workflow: Fail on error during branching
tools/workflow: Add utility git branch functions

Issue #28.
tools/worklow: Implement close()
tools/workflow: Fix fail_if_not_on_issue_branch()

This confirms that we are on an issue branch by grepping for the issue
branch prefix within the current branch name.

Issue #28.
tools/workflow: close() re-order sanity checks

We don't need to check that our tree is clean until after we have
confirmed that we're on a proper issue branch.

Issue #28.
tools/workflow: Add example usage to README

Issue #28.