add comparison note about react-like libraries

Author: chrisvfritz

src/v2/guide/comparison.md

@@ -130,6 +130,10 @@ Another option Vue developers will soon have is [NativeScript](https://www.nativ
 
 MobX has become quite popular in the React community and it actually uses a nearly identical reactivity system to Vue. To a limited extent, the React + MobX workflow can be thought of as a more verbose Vue, so if you're using that combination and are enjoying it, jumping into Vue is probably the next logical step.
 
+### Preact and Other React-Like Libraries
+
+React-like libraries usually try to share as much of their API and ecosystem with React as is feasible. For that reason, the vast majority of comparisons above will also apply to them. The main difference will typically be a reduced ecosystem, often significantly, compared to React. Since these libraries cannot be 100% compatible with everything in the React ecosystem, some tooling and companion libraries may not be usable. Or, even if they appear to work, they could break at any time unless your specific React-like library is officially supported on par with React.
+
 ## AngularJS (Angular 1)
 
 Some of Vue's syntax will look very similar to AngularJS (e.g. `v-if` vs `ng-if`). This is because there were a lot of things that AngularJS got right and these were an inspiration for Vue very early in its development. There are also many pains that come with AngularJS however, where Vue has attempted to offer a significant improvement.