I want to know the limit for API calls per minute/hour for Office365 REST APIs (Sharepoint/OneDrive).
Is there any documentation for it?
There are now throttling limits for Office 365 REST APIs. See https://msdn.microsoft.com/en-us/library/office/dn889829.aspx
Throttling can be triggered if you exceed 1 request per second continuously. You will receive a HTTP status code 429 ("Too many requests") if this happens. For your average app you are unlikely to trigger throttling. But for intensive operations you should consider handling the 429 status code and use a "backing off" algorithm like the one described in the MSDN article.