Added documentation to the fee_rate method to describe the units (sat…

…oshis/vbyte).

Update crates/bdk/src/wallet/tx_builder.rs

crates/bdk/src/wallet/tx_builder.rs

@@ -184,14 +184,15 @@ impl<'a, D, Cs: Clone, Ctx> Clone for TxBuilder<'a, D, Cs, Ctx> {
 // methods supported by both contexts, for any CoinSelectionAlgorithm
 impl<'a, D, Cs: CoinSelectionAlgorithm, Ctx: TxBuilderContext> TxBuilder<'a, D, Cs, Ctx> {
     /// Set a custom fee rate
+    /// The fee_rate method refers to the fee rate in satoshis/vbyte (sats/vbyte).
     pub fn fee_rate(&mut self, fee_rate: FeeRate) -> &mut Self {
         self.params.fee_policy = Some(FeePolicy::FeeRate(fee_rate));
         self
     }
 
     /// Set an absolute fee
     /// The fee_absolute method refers to the absolute transaction fee in satoshis (sats).
-    /// If anyone sets both the fee_absolute method and the fee_rate method, 
+    /// If anyone sets both the fee_absolute method and the fee_rate method,
     /// the fee_absolute value will take precedence over the fee_rate.
     pub fn fee_absolute(&mut self, fee_amount: u64) -> &mut Self {
         self.params.fee_policy = Some(FeePolicy::FeeAmount(fee_amount));