put links and some text into README

README.md

@@ -1,3 +1,12 @@
-# bids-specification
-
-[![Build Status](https://travis-ci.com/bids-standard/bids-specification.svg?branch=master)](https://travis-ci.com/bids-standard/bids-specification)
+[![Build Status](https://travis-ci.com/bids-standard/bids-specification.svg?branch=master)](https://travis-ci.com/bids-standard/bids-specification)
+
+# bids-specification
+
+The Brain Imaging Data Structure (BIDS) is an emerging standard for the
+organisation of neuroimaging data.
+
+In this repository, we develop the
+[BIDS specification](https://bids-specification.readthedocs.io/en/latest/).
+
+If you want to become a part of the BIDS community and contribute to the specification, please see our
+[contributing guidelines](./CONTRIBUTING.md).