Update index.md (#218)

Now mentioned directory cannot be on a cloud server

docs/source/index.md

@@ -70,7 +70,7 @@ Forest structure is based in subpackages, or *trees*, each of which addresses a
 
 ## Expected input data
 
-Input data should be included in one directory. Inside that directory, there should be a direct subdirectory corresponding to each participant ID. Inside each Beiwe ID subdirectory, there should be a direct subdirectory corresponding to each downloaded data stream.
+Input data should be included in one directory. This directory cannot be on a cloud server. Inside that directory, there should be a direct subdirectory corresponding to each participant ID. Inside each Beiwe ID subdirectory, there should be a direct subdirectory corresponding to each downloaded data stream.
 
 Methods are designed to work on data collected using the Beiwe app, with the types of sensor on/off cycles run by the Beiwe app, and with the csv files containing columns generated by Beiwe or generate data matching the data returned from the Beiwe app. Some methods included in Forest are compatible with other data collection environments, but code changes would be required to make Forest work well with those environments.