Add SwiftParser's README to the exclude list

Exclude SwiftParser's README from its target to resolve the `found 1
file(s) which are unhandled` warning.

Author: bnbarham

Package.swift

@@ -105,7 +105,10 @@ let package = Package(
     ),
     .target(
       name: "SwiftParser",
-      dependencies: ["SwiftSyntax"]
+      dependencies: ["SwiftSyntax"],
+      exclude: [
+        "README.md"
+      ]
     ),
     .executableTarget(
       name: "lit-test-helper",
@@ -173,4 +176,4 @@ if ProcessInfo.processInfo.environment["SWIFTCI_USE_LOCAL_DEPS"] == nil {
   package.dependencies += [
     .package(path: "../swift-argument-parser")
   ]
-}
+}