added nuget readme

Nuget/readme.txt

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+To update the nuget packages, follow the below procedure:
+
+1. Build the solution in release mode. This will update the contents of the dll's folder
+2. Open each nuspec file, and increment the versions of each, as well as each of the MB dependencies.
+
+For example, in MediaBrowser.Common.Internal, increment <version>, as well as <dependency id="MediaBrowser.Common" version
+
+This is quickest using notepad++. It can also be done with nuget package explorer.
+
+By keeping all the version numbers the same, it makes this largely a mindless activity. If we allow each package to have their own version, this process will be slower and prone to human error.
+
+3. Once this is done, publish the packages using nuget package explorer. File -> Publish.
+
+4. Check the nuspec files in right away, otherwise there will be merge conflicts.