Update README formatting

Author: seananderson

README.md

@@ -8,16 +8,10 @@ Course notes and exercises on ggplot2 for the FISH554 class at the University of
 
 2. Find the notes document `ggplot2-notes.pdf`. You can also download it directly from [this link](https://github.com/seananderson/ggplot2-FISH554/raw/master/ggplot2-notes.pdf).
 
-3. Install the knitr R package:
-
-```S
-install.packages("knitr")
-```
+3. Install the knitr R package: `install.packages("knitr")`
 
 4. Open the file `ggplot2-exercises.Rmd`. This is an R Markdown document. See the notes below if you're unfamiliar with it.
 
-
-
 5. Work your way through that file while you read the PDF notes document. When you want to check your work, or if you really get stuck, jump over to the [this version](https://github.com/seananderson/ggplot2-FISH554/blob/master/ggplot2-exercises-answers.md) that has the answers.
 
 ## Working with R Markdown
@@ -35,6 +29,7 @@ The basic idea is to add R code within the code chunks:
     ```{r}
     # Add your code here
     ```
+
 You can then run those code chunks, jump to chunks via the pop up menu in the bottom left of the code window, and "knit" the whole document via the "Knit HTML" button at the top of your code window.