Use standard ascii tree for directory illustration

[schlueter]

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've been mindful about doing atomic commits, adding documentation to my changes, not refactoring too much.
• I've a descriptive title and added any useful information for the reviewer. Where appropriate, I've attached a screenshot and/or screencast (gif preferably).
• I've written tests to cover the new code and functionality included in this PR. (NA)
• I've read, agree to, and signed the Contributor License Agreement (CLA).

PR Summary

Use standard ascii tree structure for directory illustration.

Related Issues

NA

Test strategy

NA

[coveralls]

Coverage remained the same at 29.268% when pulling be38ed4 on schlueter:patch-1 into 16b366a on slackhq:master.

[coveralls]

Coverage remained the same at 29.268% when pulling be38ed4 on schlueter:patch-1 into 16b366a on slackhq:master.

[coveralls]

Coverage remained the same at 29.268% when pulling be38ed4 on schlueter:patch-1 into 16b366a on slackhq:master.