update readme

README.md

@@ -8,7 +8,7 @@ swirl is a platform for learning (and teaching) statistics and R simultaneously
 
 swirl leans heavily on exercising a student's use of the R console. A callback mechanism, suggested and first demonstrated for the purpose by Hadley Wickham, is used to capture student input and to provide immediate feedback relevant to the course material at hand.
 
-[swirlify](https://github.com/swirldev/swirlify) is a separate R package that provides a comprehensive toolbox for swirl instructors. Course authoring is possible in a variety of formats including [R Markdown](http://www.rstudio.com/ide/docs/r_markdown), [YAML](http://en.wikipedia.org/wiki/YAML), and [CSV](http://en.wikipedia.org/wiki/Comma-separated_values). Documentation for authoring content in R Markdown can be found on the [Instructors page](http://swirlstats.com/instructors.html) of our website.
+[swirlify](https://github.com/swirldev/swirlify) is a separate R package that provides a comprehensive toolbox for swirl instructors. Content is authored in [YAML](http://en.wikipedia.org/wiki/YAML) using the handy tools described on the [instructors page](http://swirlstats.com/instructors.html) of our website.
 
 The program is initiated with `swirl()`. Functions which control swirl's behavior include `bye()` to quit, `skip()` to skip a question, `main()` to return to the main menu, `play()` to allow experimentation in the R console without interference from swirl, `nxt()` to resume interacting with swirl, and `info()` to display a help menu.
 
@@ -27,14 +27,15 @@ As we continue adding new features and content, we will make new versions availa
 
 ## Installing the latest development version (from GitHub)
 
-To access the most recent features and content, or to contribute to swirl's development, you can install and run the development version of swirl using the [devtools](https://github.com/hadley/devtools) package:
+To access the most recent features and content, you can install and run the development version of swirl using the [devtools](https://github.com/hadley/devtools) package:
 
 ```
 install.packages("devtools")
-library(devtools)
-install_github("swirldev/swirl")
+devtools::install_github("swirldev/swirl")
 library(swirl)
 swirl()
 ```
 
-Note: If `install_github("swirldev/swirl")` gives you an error, try `install_github(username="swirldev", repo="swirl")` instead.
+## Contributing to swirl's development
+
+If you'd like to get involved, please fork this repository and submit a pull request with your proposed changes. We're happy to chat if you have any questions about the source code.