Add comment about unexpected assertion

app/src/test/java/org/schabi/newpipe/util/LocalizationTest.kt

@@ -18,6 +18,7 @@ class LocalizationTest {
 
         val actual = Localization.relativeTime(GregorianCalendar(2021, 1, 6))
 
+        // yes this assertion is true, even if it should be 5 days, it works as it is. Future research required.
         assertEquals("1 month from now", actual)
     }