Update readme for CRAN release

README.md

@@ -1,6 +1,7 @@
 # dtplyr
 
 [![Travis-CI Build Status](https://travis-ci.org/hadley/dtplyr.svg?branch=master)](https://travis-ci.org/hadley/dtplyr)
+[![CRAN_Status_Badge](http://www.r-pkg.org/badges/version/dtplyr)](https://cran.r-project.org/package=dtplyr)
 [![Coverage Status](https://img.shields.io/codecov/c/github/hadley/dtplyr/master.svg)](https://codecov.io/github/hadley/dtplyr?branch=master)
 
 dtplyr is the data.table backend for dplyr. It provides S3 methods for data.table objects so that dplyr works the way you expect. 
@@ -11,7 +12,13 @@ dtplyr was extracted out of dplyr so it could evolve independently (i.e. more ra
 
 ## Installation
 
-You can install from Github with:
+You can install from CRAN with:
+
+```R
+install.packages("dtplyr")
+```
+
+Or try the development version from GitHub with:
 
 ```R
 # install.packages("devtools")