Updated the README with the new TLD for RTD

README.md

@@ -1,3 +1,3 @@
 This Python package is intended for analysis of data from the [GRIPS](http://grips.ssl.berkeley.edu) long-duration flight of 2016 January 19–30.  It can also be used to analyze the pre-flight calibration data that was already being recorded using flight-like packet formats.  The code is still very much a work in progress, so not only are many elements still missing, even the parts that have been coded are likely to go through changes in their interfaces and organization.
 
-The documentation can be found here: http://gripspy.readthedocs.org
+The documentation can be found here: http://gripspy.readthedocs.io