docs(README): add Cannot capture not invokable method error to FAQ

closes #36

Author: twada

README.md

@@ -137,6 +137,7 @@ FAQ
 - [Are all dependencies required at runtime?](https://github.com/power-assert-js/power-assert/issues/24)
 - [Descriptive assertion message does not appear when writing tests in ES6 with Babel](https://github.com/power-assert-js/webpack-espower-loader/issues/4#issuecomment-139605343)
 - [Incomplete increment/decrement assertion messages?](https://github.com/power-assert-js/power-assert/issues/32)
+- [Cannot capture not invokable method error](https://github.com/power-assert-js/power-assert/issues/36)
 
 
 EXAMPLE