describe "explicit declaration" fix for Swift 5.2

Added notes about fixing the "dependency requires explicit declaration" error when using recent versions of Swift Package Manager until swift-sh fixes its issue #111

README.md

@@ -34,3 +34,38 @@ struct RenameMoviesCommand: ParsableCommand {
 
 RenameMoviesCommand.main()
 ```
+
+## Note for swift-sh 1.17.1 and recent versions of Swift Package Manager
+Until swift-sh issue #111 https://github.com/mxcl/swift-sh/issues/111 is fixed and if you're using SPM from Swift 5.2 (Xcode 11.4 or later) then any script using RenameCommand will fail to build with a "dependency requires explicit declaration" error and output like this:
+
+    Updating https://github.com/jpmhouston/RenameCommand.git
+    Updating https://github.com/JohnSundell/Files
+    Updating https://github.com/sharplet/Regex.git
+    Updating https://github.com/apple/swift-argument-parser.git
+    Resolving https://github.com/jpmhouston/RenameCommand.git at 4c299aa2e4ff571893b18ac71aa39a195cb09bb1
+    'renametest' /Users/me/Library/Developer/swift-sh.cache/98d753591fe20951a239e2e2b1a6cc12: error: dependency 'ArgumentParser' in target 'renametest' requires explicit declaration; reference the package in the target dependency with '.product(name: "ArgumentParser", package: "swift-argument-parser")'
+    error: 1 <(/usr/bin/swift build -Xswiftc -suppress-warnings)
+
+You'll need to copy the `swift-sh.cache` path out of that error and edit the file `Package.swift` in that directory, for example:
+
+    vi /Users/me/Library/Developer/swift-sh.cache/98d753591fe20951a239e2e2b1a6cc12/Package.swift
+
+In `Package.swift` the occurance of `"ArgumentParser"` must be replaced with `.product(name: "ArgumentParser", package: "swift-argument-parser")`.
+
+Explicitly, replace:
+
+    pkg.targets = [
+        .target(name: "rename-tv", dependencies: ["ArgumentParser", "RenameCommand", "Regex"], path: ".", sources: ["main.swift"])
+    ]
+
+with (I've expanded the inner array onto multiple lines):
+
+    pkg.targets = [
+        .target(name: "rename-tv", dependencies: [
+            .product(name: "ArgumentParser", package: "swift-argument-parser"),
+            "RenameCommand",
+            "Regex"
+        ], path: ".", sources: ["main.swift"])
+    ]
+
+Save this and build / run the script again and it should work. Unfortunately if any of those packages are updated in the future before swift-sh #111 is fixed you'll need to make this same edit again. You may want to explicitly fix the dependency versions in your `import` line comments to prevent this, see examples in the readme at https://github.com/mxcl/swift-sh.