add images for fixed vs geared bicycle analogy see: #34 (comment)

tap-advanced-testing.md

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+# _Why_ Use `Tap`?
+
+In _most_ situations **`Tape`** will be _exactly_ what you need
+to write and run your Node.js (server-side) tests.
+**`Tape`** is minimalist, fast and has plenty of flexibility.
+_Occasionally_ however, the needs of the project
+require a few extra features of the testing framework.
+
+
+## Analogy: _Single_ Speed vs. _Geared_ Bicycle
+
+![sku-fixie-single-speed-bike](https://user-images.githubusercontent.com/194400/46041154-102cb800-c10a-11e8-8646-153a77b53408.jpg)
+
+![specialised-racing-bicycle](https://user-images.githubusercontent.com/194400/46041153-102cb800-c10a-11e8-9c51-3c16eb81db4c.jpg)