This is NOT an error, merely a warning. You can still compile, debug & run your application on emulators / devices. When you export your application to create a release build, by default this APK is NOT debuggable, since this APK will be released to users, but the APK you are currently building is debugabble by default, so if you wish you can remove the android:debuggable tag.
References:
1. SDK Tools
In the above link go to SDK Tools, Revision 8 and there see General Notes.
2. Setting up a Device for Development