Impove rustdoc on assume_checked_ref

Add a newline to separate the body and heading of function rustdoc.

bitcoin/src/address/mod.rs

@@ -631,10 +631,12 @@ impl Address {
 /// Methods that can be called only on `Address<NetworkUnchecked>`.
 impl Address<NetworkUnchecked> {
     /// Returns a reference to the checked address.
+    ///
     /// This function is dangerous in case the address is not a valid checked address.
     pub fn assume_checked_ref(&self) -> &Address {
         unsafe { &*(self as *const Address<NetworkUnchecked> as *const Address) }
     }
+
     /// Parsed addresses do not always have *one* network. The problem is that legacy testnet,
     /// regtest and signet addresse use the same prefix instead of multiple different ones. When
     /// parsing, such addresses are always assumed to be testnet addresses (the same is true for