Added a better README.

README.md

@@ -1,3 +1,22 @@
 #rUMLS
 An R interface for the National Library of Medicine's Unified Medical Language System [UMLS](https://www.nlm.nih.gov/research/umls/).
 
+## Installation
+
+This currently can only be installed from github:
+
+```R
+# install.packages('devtools')
+devtools::install_github("mpancia/rUMLS")
+```
+
+## Authentication
+
+You need an NLM license in order to use this package. Obtain one at [the NLM site](https://uts.nlm.nih.gov/home.html#). 
+
+## Useful links
+
+* [Metathesaurus Reference](http://www.ncbi.nlm.nih.gov/books/NBK9684/)
+* [API Reference](https://www.nlm.nih.gov/api/)
+* [UMLS Login](https://www.nlm.nih.gov/research/umls/)
+* [UMLS Quickstart Login](https://www.nlm.nih.gov/research/umls/quickstart.html)