Auto merge of rust-lang#6390 - pro-grammer1:master, r=ebroto

Added known problem to comparison_chain docs

changelog: Added documentation to comparison_chain that explains a possible performance penalty, according to issue rust-lang#5354

This is my first PR, I hope everything has been done correctly.

Fixes rust-lang#5354

Author: bors

clippy_lints/src/comparison_chain.rs

@@ -12,7 +12,8 @@ declare_clippy_lint! {
     /// **Why is this bad?** `if` is not guaranteed to be exhaustive and conditionals can get
     /// repetitive
     ///
-    /// **Known problems:** None.
+    /// **Known problems:** The match statement may be slower due to the compiler
+    /// not inlining the call to cmp. See issue #5354
     ///
     /// **Example:**
     /// ```rust,ignore