minor update to the doc to include cats-testkit-scalatest (#3049)

README.md

@@ -110,6 +110,7 @@ functionality, you can pick-and-choose from amongst these modules
  * [`kittens`](https://github.com/typelevel/kittens): automatic type class instance derivation for Cats and generic utility functions
  * [`cats-tagless`](https://github.com/typelevel/cats-tagless): Utilities for tagless final encoded algebras
  * [`cats-collections`](https://github.com/typelevel/cats-collections): Data structures which facilitate pure functional programming
+ * [`cats-testkit-scalatest`](https://github.com/typelevel/cats-testkit-scalatest): Cats testkit integration with Scalatest
 
 Past release notes for Cats are available in [CHANGES.md](https://github.com/typelevel/cats/blob/master/CHANGES.md).
 See [Cats 2019 roadmap](https://github.com/typelevel/cats/blob/master/ROADMAP_2019.md) for our plan for 2019.

docs/src/main/tut/typeclasses/lawtesting.md

@@ -19,8 +19,8 @@ To make things easier, we'll also include the `scalacheck-shapeless` library in
 
 ```scala
 libraryDependencies ++= Seq(
-  "org.typelevel" %% "cats-laws" % "1.1.0" % Test,
-  "com.github.alexarchambault" %% "scalacheck-shapeless_1.13" % "1.1.6" % Test
+  "org.typelevel" %% "cats-laws" % "2.0.0" % Test,
+  "com.github.alexarchambault" %% "scalacheck-shapeless_1.14" % "1.2.3" % Test
 )
 ```
 
@@ -109,6 +109,9 @@ class TreeLawTests extends AnyFunSuite with Discipline {
 * `Discipline` provides `checkAll`, and must be mixed into `AnyFunSuite`
 * `arbitraries._` imports the `Arbitrary[Tree[_]]` instances needed to check the laws.
 
+Alternatively, you can use the `CatsSuite` provided by [Cats-testkit-scalatest](https://github.com/typelevel/cats-testkit-scalatest), 
+which is the same `CatsSuite` used in Cats to test all instances.  
+
 Now when we run `test` in our sbt console, ScalaCheck will test if the `Functor` laws hold for our `Tree` type.
 You should see something like this: