Add more display examples to README and documentation

Author: sunsided

README.md

@@ -11,12 +11,13 @@ use query_string_builder::QueryString;
 fn main() {
     let qs = QueryString::new()
         .with_value("q", "apple")
+        .with_value("tasty", true)
         .with_opt_value("color", None::<String>)
         .with_opt_value("category", Some("fruits and vegetables?"));
 
     assert_eq!(
         format!("https://example.com/{qs}"),
-        "https://example.com/?q=apple&category=fruits%20and%20vegetables?"
+        "https://example.com/?q=apple&tasty=true&category=fruits%20and%20vegetables?&tasty=true"
     );
 }
 ```

src/lib.rs

@@ -10,12 +10,13 @@
 //!
 //! let qs = QueryString::new()
 //!             .with_value("q", "🍎 apple")
+//!             .with_value("tasty", true)
 //!             .with_opt_value("color", None::<String>)
 //!             .with_opt_value("category", Some("fruits and vegetables?"));
 //!
 //! assert_eq!(
 //!     format!("example.com/{qs}"),
-//!     "example.com/?q=%F0%9F%8D%8E%20apple&category=fruits%20and%20vegetables?"
+//!     "example.com/?q=%F0%9F%8D%8E%20apple&tasty=true&category=fruits%20and%20vegetables?"
 //! );
 //! ```