Examples fixes for regex (rust-lang#13874)

Examples fixes for regex

changelog: none

Author: dswij

clippy_lints/src/regex.rs

@@ -24,6 +24,11 @@ declare_clippy_lint! {
     /// ```ignore
     /// Regex::new("(")
     /// ```
+    ///
+    /// Use instead:
+    /// ```ignore
+    /// Regex::new("\(")
+    /// ```
     #[clippy::version = "pre 1.29.0"]
     pub INVALID_REGEX,
     correctness,
@@ -49,6 +54,11 @@ declare_clippy_lint! {
     /// ```ignore
     /// Regex::new("^foobar")
     /// ```
+    ///
+    /// Use instead:
+    /// ```ignore
+    /// str::starts_with("foobar")
+    /// ```
     #[clippy::version = "pre 1.29.0"]
     pub TRIVIAL_REGEX,
     nursery,