Add darling to "macros helpers" section

It's an absolute must when writing derive macros. It makes writing them 10x easier.
It has 8M downloads a month and is top 10 in "Rust patterns" on lib.rs.

https://lib.rs/crates/darling

data/crates.json

@@ -337,6 +337,9 @@
                             }, {
                                 "name": "paste",
                                 "notes": "Concatenating and manipulating identifiers"
+                            }, {
+                                "name": "darling",
+                                "notes": "Derive macro to easily parse derive macro inputs"
                             }]
                         },
                         {