Fix compiler plugin instruction in README

[ncreep]

[cvogt]

Shapeless mentions this as the instructions for 2.10:

scalaVersion := "2.10.6"

libraryDependencies ++= Seq(
  "com.chuusai" %% "shapeless" % "2.3.1",
  compilerPlugin("org.scalamacros" % "paradise" % "2.1.0" cross CrossVersion.full)
)

I obviously was a bit briefer. Does the addCompilerPlugin work as well? Are they equivalent?

[ncreep]

Oh, my bad. I wasn't aware of this syntax and couldn't get it to work. addCompilerPlugin works differently, you just put it in the file anywhere and it works (without adding to libraryDependencies).

[cvogt]

Other people may have the same misunderstanding. And I actually hadn't heard of compilerPlugin before I looked at the shapeless docs myself. Will re-open and probably adjust docs.