This message is a warning which says that your new apk will be available for a fewer number of devices.
The reason is, you made changes which probably affected AndroidManifest.xml. You could add new permissions, feature, screen support etc. So this message will be helpful when you added one of them by mistake and you would make apk available for fewer people (who would like to do that by mistake?).
Go through your code changes (comparing to the previous build) to check what exactly makes this limitation happened.
In most of the cases it's totally fine, because it's just natural that during the development process, you request more regarding system or device and as a result, it will run on a smaller number of devices.
You can ignore this warning and go ahead with publishing if you're aware what you're doing.
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
