add an example to print the Fq and Fr of all the Arkworks' curves

examples/curves.rs

+use ark_ff::PrimeField;
+
+fn show_curve<Fr: PrimeField, Fq: PrimeField>(name: &str) {
+    println!(
+        "{}: {} -> {}",
+        name,
+        Fq::MODULUS_BIT_SIZE,
+        Fr::MODULUS_BIT_SIZE
+    );
+}
+
+macro_rules! show_curve {
+    ($($c:ident),+ $(,)?) => {
+        $(show_curve::<$c::Fr, $c::Fq>(stringify!($c));)*
+    }
+}
+
+fn main() {
+    show_curve!(
+        ark_bls12_377,
+        ark_bls12_381,
+        ark_bn254,
+        ark_bw6_761,
+        ark_cp6_782,
+        ark_curve25519,
+        ark_ed_on_bls12_377,
+        ark_ed_on_bls12_381,
+        ark_ed_on_bls12_381_bandersnatch,
+        ark_ed_on_bn254,
+        ark_ed_on_bw6_761,
+        ark_ed_on_cp6_782,
+        ark_ed_on_mnt4_298,
+        ark_ed_on_mnt4_753,
+        ark_ed25519,
+        ark_mnt4_298,
+        ark_mnt4_753,
+        ark_mnt6_298,
+        ark_mnt6_753,
+        ark_pallas,
+        ark_secp256k1,
+        ark_secp256r1,
+        ark_secp384r1,
+        ark_secq256k1,
+        ark_vesta,
+    );
+}