Update nuspec (#82)

***NO_CI***

Author: josesimoes

nanoFramework.Networking.Sntp.nuspec

@@ -13,10 +13,11 @@
     <developmentDependency>false</developmentDependency>
     <projectUrl>https://github.com/nanoframework/lib-nanoFramework.Networking.Sntp</projectUrl>
     <iconUrl>https://secure.gravatar.com/avatar/97d0e092247f0716db6d4b47b7d1d1ad</iconUrl>
+    <icon>images\nf-logo.png</icon>
     <repository type="git" url="https://github.com/nanoframework/lib-nanoFramework.Networking.Sntp" commit="$commit$" />
     <copyright>Copyright (c) 2018 The nanoFramework project contributors</copyright>
     <description>This package includes the nanoFramework.Networking.Sntp assembly for nanoFramework C# projects.
-This package requires a target with nanoFramework.Networking.Sntp v$nativeVersion$.</description>
+This package requires a target with nanoFramework.Networking.Sntp v$nativeVersion$ (checksum $checksum$).</description>
     <summary>nanoFramework.Networking.Sntp assembly for nanoFramework C# projects</summary>
     <tags>nanoFramework C# csharp netmf netnf nanoFramework.Networking.Sntp sntp</tags>
     <dependencies>
@@ -31,5 +32,6 @@ This package requires a target with nanoFramework.Networking.Sntp v$nativeVersio
     <file src="nanoFramework.Networking.Sntp\bin\Release\nanoFramework.Networking.Sntp.xml" target="lib\nanoFramework.Networking.Sntp.xml" />
     <!-- readme -->
     <file src="readme.txt" target="readme.txt" />
+    <file src="nanoFramework.Networking.Sntp\nf-logo.png" target="images\" />
   </files>
 </package>