cargo.toml: moved drk, darkfid and gateway to 'workspace'

Cargo.toml

@@ -88,6 +88,10 @@ libsqlite3-sys = {version = "0.23.1", features = ["bundled-sqlcipher"],  optiona
 zeromq = {version = "0.3.1", default-features = false, features = ["async-std-runtime", "all-transport"],  optional = true }
 signal-hook-async-std = {version = "0.2.1", optional = true}
 
+[workspace]
+members = ["bin/drk", "bin/darkfid", "bin/gateway"]
+exclude = ["bin/cashier"]
+
 [features]
 chain = ["rocksdb"]
 node = ["sqlx", "libsqlite3-sys", "zeromq", "signal-hook-async-std"]