Add known problems to mut_range_bound docs

Author: dswij

clippy_lints/src/loops/mod.rs

@@ -397,6 +397,10 @@ declare_clippy_lint! {
     /// ### Why is this bad?
     /// One might think that modifying the mutable variable changes the loop bounds
     ///
+    /// ### Known problems
+    /// False positive when mutation is not immediately followed by a break statement
+    /// False positive on nested expressions ([#6072](https://github.com/rust-lang/rust-clippy/issues/6072))
+    ///
     /// ### Example
     /// ```rust
     /// let mut foo = 42;