Update Readme.md

rmd_reader/Readme.md

@@ -13,9 +13,32 @@ Install it with:
 pip install rpy2
 ```
 
+Of course, R must be installed and also the knitr package.
+Execute the command below in R to get knitr installed.
+
+```
+R> install.packages('knitr')
+```
+
 ## Usage
 
-The plugin detects RMD files ending with `.Rmd` or `.rmd` so you only have to write a RMarkdown files inside content directory.
+The plugin detects RMD files ending with `.Rmd` or `.rmd` so you only have to write a RMarkdown files inside `content` directory.
 
 This plugin calls R to process these files and generates markdown files that are processed by Python Markdown (with `meta`, `codehilite(css_class=highlight)`, and `extra` extensions) before returning the content and metadata to pelican engine.
 
+### Plotting
+
+The code below must be pasted inside the `.Rmd` file in order to correctly set the `src` attribute of `img` tag.
+
+	```{r, echo=FALSE}
+	hook_plot <- knit_hooks$get('plot')
+	knit_hooks$set(plot=function(x, options) {
+	    if (!is.null(options$pelican.publish) && options$pelican.publish) {
+	        x <- paste0("{filename}", x)
+	    }
+	    hook_plot(x, options)
+	})
+	opts_chunk$set(pelican.publish=TRUE)
+	```
+
+I usually paste it just after the Markdown header.