redirect 'documentation/package-manager' (#1125)

* redirect 'documentation/package-manager' to 'https://docs.swift.org/swiftpm/documentation/packagemanagerdocs/'
* making the just-in-case content a complete sentence
* leverage the redirectTo: plugin

Author: heckj

documentation/package-manager/_basic-usage.md

@@ -2,31 +2,10 @@
 redirect_from: "/package-manager/"
 layout: page
 title: Package Manager
+redirect_to: https://docs.swift.org/swiftpm/documentation/packagemanagerdocs/
 ---
+<meta http-equiv="refresh" content="0; url=https://docs.swift.org/swiftpm/documentation/packagemanagerdocs/">
+<link rel="canonical" href="https://docs.swift.org/swiftpm/documentation/packagemanagerdocs/" />
 
-The Swift Package Manager (SwiftPM) is a tool for managing the distribution of Swift code.
-It's integrated with the Swift build system
-to automate the process of downloading, compiling, and linking dependencies.
-
-The Package Manager is included in Swift 3.0 and above.
-
-{% include_relative _conceptual-overview.md %}
-
-* * *
-
-<div class="info" markdown="1">
-The following section assumes a working knowledge of Swift.
-If you're new to the language,
-you may want consult one of the introductory resources first.
-We recommend [A Swift Tour][TSPL] in
-_The Swift Programming Language_.
-
-If you want to follow along with the code examples,
-you'll need to have a working installation of Swift.
-You can find instructions for how to install Swift in
-[Getting Started](/getting-started/#installing-swift).
-</div>
-
-{% include_relative _basic-usage.md %}
-
-[TSPL]: https://docs.swift.org/swift-book/documentation/the-swift-programming-language/
+This page should redirect automatically to the updated location for
+the [Swift Package Manager (SwiftPM) documentation](https://docs.swift.org/swiftpm/documentation/packagemanagerdocs/).