Keep Known Problems documentation in redundant_pattern_matching

Author: flip1995

clippy_lints/src/matches.rs

@@ -424,7 +424,12 @@ declare_clippy_lint! {
     /// **Why is this bad?** It's more concise and clear to just use the proper
     /// utility function
     ///
-    /// **Known problems:** None.
+    /// **Known problems:** This will change the drop order for the matched type. Both `if let` and
+    /// `while let` will drop the value at the end of the block, both `if` and `while` will drop the
+    /// value before entering the block. For most types this change will not matter, but for a few
+    /// types this will not be an acceptable change (e.g. locks). See the
+    /// [reference](https://doc.rust-lang.org/reference/destructors.html#drop-scopes) for more about
+    /// drop order.
     ///
     /// **Example:**
     ///