Add a NuGet package specification

Work towards resolving #13.

PowerShell-FeatureFlags.nuspec

@@ -0,0 +1,21 @@
+<?xml version="1.0"?>
+<package xmlns="http://schemas.microsoft.com/packaging/2010/07/nuspec.xsd">
+  <metadata>
+    <id>PowerShell-FeatureFlags</id>
+    <version>1.0.0</version>
+    <title>PowerShell Feature Flags</title>
+    <authors>Andrea Spadaccini,Nick Hara</authors>
+    <owners>Andrea Spadaccini</owners>
+    <licenseUrl>https://github.com/microsoft/PowerShell-FeatureFlags/blob/master/LICENSE</licenseUrl>
+    <projectUrl>https://github.com/microsoft/PowerShell-FeatureFlags/</projectUrl>
+    <requireLicenseAcceptance>false</requireLicenseAcceptance>
+    <description>PowerShell module containing a Feature Flags implementation based on a local config file.</description>
+    <releaseNotes>First release.</releaseNotes>
+    <copyright>Copyright 2019</copyright>
+    <repository type="git" url="https://github.com/microsoft/PowerShell-FeatureFlags.git" branch="master" />
+  </metadata>
+  <files>
+    <file src="bld\psgallery\FeatureFlags\*.*" target="$targetBase$" />
+    <file src="bld\psgallery\FeatureFlags\External\**\netstandard1.0\*.*" target="$targetBase$\External" />
+  </files>
+</package>