docs: add guiding principles to readme

Author: bcarroll22

README.md

@@ -42,6 +42,8 @@
 - [Hooks](#hooks)
 - [Inspiration](#inspiration)
 - [Other Solutions](#other-solutions)
+- [Guiding Principles](#guiding-principles)
+- [Contributors](#contributors)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
@@ -167,6 +169,27 @@ The awesome engineers at [Callstack](https://callstack.com/) built a similar pac
 If you find yourself needing things like shallow rendering and the ability to query elements
 by type and props, you'll definitely want to check it out!
 
+## Guiding Principles
+
+> [The more your tests resemble the way your software is used, the more confidence they can give you.](https://twitter.com/kentcdodds/status/977018512689455106)
+
+We try to only expose methods and utilities that encourage you to write tests that closely resemble
+how your apps are used.
+
+Utilities are included in this project based on the following guiding principles:
+
+1.  If it relates to rendering components, it deals with native views rather than component
+    instances, nor should it encourage dealing with component instances.
+2.  It should be generally useful for testing the application components in the way the user would
+    use it. We are making some trade-offs here because we're using a computer and often a simulated
+    environment, but in general, utilities should encourage tests that use the components the way
+    they're intended to be used.
+3.  Utility implementations and APIs should be simple and flexible.
+
+In summary, we believe in the principles of `testing-library`, and adhere to them as closely as
+possible. At the end of the day, what we want is for this library to be pretty light-weight, simple,
+and understandable.
+
 ## Contributors
 
 Thanks goes to these wonderful people ([emoji key](https://allcontributors.org/docs/en/emoji-key)):