Add Verilator dependency (#123)

Update README.md to indicate that Verilator is now necessary for testing.

README.md

@@ -11,13 +11,18 @@ with a clean running [Chisel3](https://www.chisel-lang.org/) project.
 
 #### JDK 8 or newer
 
-We recommend LTS releases Java 8 and Java 11. You can install the JDK as recommended by your operating system, or use the prebuilt binaries from [AdoptOpenJDK](https://adoptopenjdk.net/).
+We recommend LTS releases Java 8 and Java 11. You can install the JDK as your operating system recommends, or use the prebuilt binaries from [AdoptOpenJDK](https://adoptopenjdk.net/).
 
 #### SBT or mill
 
-SBT is the most common built tool in the Scala community. You can download it [here](https://www.scala-sbt.org/download.html).  
+SBT is the most common build tool in the Scala community. You can download it [here](https://www.scala-sbt.org/download.html).  
 mill is another Scala/Java build tool without obscure DSL like SBT. You can download it [here](https://github.com/com-lihaoyi/mill/releases)
 
+#### Verilator
+
+The test with `svsim` needs Verilator installed.
+See Verilator installation instructions [here](https://verilator.org/guide/latest/install.html).
+
 ### How to get started
 
 #### Create a repository from the template