Update stale_deps.jl

src/stale_deps.jl

@@ -12,6 +12,12 @@ directly, this can be achieved via transitivity as well.
     not check if a package extension indeed loads all of its trigger
     dependencies using `import` or `using`. 
 
+!!! warning "Known bug"
+    Currently, `Aqua.test_stale_deps` does not detect stale
+    dependencies when they are in the sysimage. This is considered a 
+    bug and may be fixed in the future. Such a release is considered
+    non-breaking.
+
 # Arguments
 - `packages`: a top-level `Module`, a `Base.PkgId`, or a collection of
   them.