spm: complex refactor, document of package

Tuist/Setup.swift

@@ -0,0 +1,21 @@
+import ProjectDescription
+
+let setup = Setup(
+    require: [
+        .precondition( 
+            .swiftVersion("5.3.2"), 
+            .xcodeVersion("12.4", "12D4e"))
+    ],
+    run: [
+        .homebrew(packages: [
+            "rustup-init", 
+            "rust", 
+            "cargo-c", 
+            "swiftformat", 
+            "swiftlint", 
+            "swiftgen", 
+            "swift-doc"
+        ]),
+        .mint()
+    ]
+)