Add a note about `ReportSenderException`

[GregCornis]

acra-http throws a ReportSenderException if it fails to send the report, so I imagine it's a mechanism to allow for a later retry. ACRA's message is pretty clear: org.acra.sender.ReportSenderException: Policy marked this task as incomplete. ACRA will try to send this report again.

I thought it would be nice to document it. It might need to be rephrased.

[F43nd1r]

Depending on the RetryPolicy, the sentence you added might not be true. Default behaviour is to only retry when all senders failed. Of course most setups will only use one sender and the default policy, in which case your statement is true.

[GregCornis]

How about

You can implement your own ReportSender and configure ACRA to use that instead of or in addition to other senders. Note: Throwing a ReportSenderException from YourCustomSender.send() notifies ACRA of a failed delivery, and might trigger a retry (see RetryPolicy).