Add summary for the Hangfire NuGet package

nuspecs/Hangfire.nuspec

@@ -9,6 +9,7 @@
     <projectUrl>http://hangfire.io/</projectUrl>
     <requireLicenseAcceptance>false</requireLicenseAcceptance>
     <licenseUrl>https://raw.github.com/HangfireIO/Hangfire/master/LICENSE.md</licenseUrl>
+    <summary>An easy way to perform fire-and-forget, delayed and recurring tasks inside ASP.NET applications. No Windows Service required.</summary>
     <description>
       An easy and reliable way to perform fire-and-forget, delayed and recurring long-running, short-running, CPU or I/O intensive tasks inside ASP.NET application. No Windows Service / Task Scheduler required. Even ASP.NET is not required.
       Backed by Redis, SQL Server, SQL Azure or MSMQ. This is a .NET alternative to Sidekiq, Resque and Celery.