[build] Emit a message if liburing subproject is used

meson.build

@@ -9,8 +9,11 @@ project('EMPER', 'c', 'cpp',
 		])
 
 thread_dep = dependency('threads')
-uring_dep = dependency('liburing', version: '2.0', required: false)
+
+liburing_version = '2.0'
+uring_dep = dependency('liburing', version: liburing_version, required: false)
 if not uring_dep.found()
+	message('liburing ' + liburing_version + ' not found in system, using liburing subproject')
 	liburing_sp = subproject('liburing')
 	uring_dep = liburing_sp.get_variable('uring').as_system()
 endif