Document cargo features

Credit to @hinto-janai for adding such sections to their work on documenting
monero-serai in #568.

coins/monero/wallet/README.md

@@ -46,3 +46,13 @@ monero-serai.
 
 Finally, this library only supports producing transactions with CLSAG
 signatures. That means this library cannot spend non-RingCT outputs.
+
+### Cargo Features
+
+- `std` (on by default): Enables `std` (and with it, more efficient internal
+  implementations).
+- `compile-time-generators` (on by default): Derives the generators at
+  compile-time so they don't need to be derived at runtime. This is recommended
+  if program size doesn't need to be kept minimal.
+- `multisig`: Adds support for creation of transactions using a threshold
+  multisignature wallet.

coins/monero/wallet/address/README.md

@@ -4,3 +4,8 @@ Rust implementation of [Polyseed](https://github.com/tevador/polyseed).
 
 This library is usable under no-std when the `std` feature (on by default) is
 disabled.
+
+### Cargo Features
+
+- `std` (on by default): Enables `std` (and with it, more efficient internal
+  implementations).

coins/monero/wallet/polyseed/README.md

@@ -4,3 +4,8 @@ Rust implementation of [Polyseed](https://github.com/tevador/polyseed).
 
 This library is usable under no-std when the `std` feature (on by default) is
 disabled.
+
+### Cargo Features
+
+- `std` (on by default): Enables `std` (and with it, more efficient internal
+  implementations).

coins/monero/wallet/seed/README.md

@@ -4,3 +4,8 @@ Rust implementation of Monero's seed algorithm.
 
 This library is usable under no-std when the `std` feature (on by default) is
 disabled.
+
+### Cargo Features
+
+- `std` (on by default): Enables `std` (and with it, more efficient internal
+  implementations).

coins/monero/wallet/util/README.md

@@ -13,3 +13,13 @@ disabled.
 
 - Support for Monero's seed algorithm
 - Support for Polyseed
+
+### Cargo Features
+
+- `std` (on by default): Enables `std` (and with it, more efficient internal
+  implementations).
+- `compile-time-generators` (on by default): Derives the generators at
+  compile-time so they don't need to be derived at runtime. This is recommended
+  if program size doesn't need to be kept minimal.
+- `multisig`: Adds support for creation of transactions using a threshold
+  multisignature wallet.