Auto merge of #7065 - rail-rain:warn_copy_pass_by_ref, r=Manishearth

Add a note on the issue #5953

Hello,

I thought it would be better to have a note and warning about this issue considering it introduced an UB in the past even with the "Search on Github" feature.

---

changelog: Add a note on the issue #5953 to the known problems section.

clippy_lints/src/pass_by_ref_or_value.rs

@@ -42,6 +42,14 @@ declare_clippy_lint! {
     /// false positives in cases involving multiple lifetimes that are bounded by
     /// each other.
     ///
+    /// Also, it does not take account of other similar cases where getting memory addresses
+    /// matters; namely, returning the pointer to the argument in question,
+    /// and passing the argument, as both references and pointers,
+    /// to a function that needs the memory address. For further details, refer to
+    /// [this issue](https://github.com/rust-lang/rust-clippy/issues/5953)
+    /// that explains a real case in which this false positive
+    /// led to an **undefined behaviour** introduced with unsafe code.
+    ///
     /// **Example:**
     ///
     /// ```rust