adds citations to features in readme

README.md

@@ -20,6 +20,7 @@ The default features include:
   - how to insert tables from CSV files
   - how to insert flowcharts generated via [Graphviz][] from `.dot` sources
   - how to insert plots generated with [R][] from CSV sources
+  - how to use citations using a shared reference database
 - a build script (`Makefile`) to automate the build process
 - convert Markdown sources to PDF with [pandoc][]
 - continuous integration, i.e. a build server that automatically