Added to README, really just needed a change of any sort

### Nuget package appears to be broken and needs an update

Github removed the messaging system, not sure how else to get a hold of the maintainer of this
package. As such this pull request is really just for the purpose of sending a message to synhershko.

On Nuget: Spatial4n.Core.NTS has a dependency of NetTopologySuite >= 1.12.0 listed.
However, if I try to use the assembly with NetTopologySuite 1.13.2.0 (the current Nuget package),
A version mismatch exception is thrown.

I compiled Spatial4n from source and replaced the Nuget version in my project with it, which
fixes the issue. It appears there is a hard coded version requirement in the current Nuget package.

Anyway, just a heads up :)

Exception is as follows:
~~~~
System.TypeInitializationException was unhandled by user code
  HResult=-2146233036
  Message=The type initializer for 'Spatial4n.Core.Context.Nts.NtsSpatialContext' threw an exception.
  Source=Go2It
  TypeName=Spatial4n.Core.Context.Nts.NtsSpatialContext
  StackTrace:
       at Go2It.AdminForm.GetDocuments(IndexObject[] iobjects) in H:\Workspace\dotspatial-go2it\src\AdminForm.cs:line 1634
       at Go2It.AdminForm.btnCreateIndex_Click(Object sender, EventArgs e) in H:\Workspace\dotspatial-go2it\src\AdminForm.cs:line 1552
       at System.Windows.Forms.Control.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnClick(EventArgs e)
       at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
       at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
       at System.Windows.Forms.Control.WndProc(Message& m)
       at System.Windows.Forms.ButtonBase.WndProc(Message& m)
       at System.Windows.Forms.Button.WndProc(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
       at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
       at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
  InnerException: System.IO.FileLoadException
       HResult=-2146234304
       Message=Could not load file or assembly 'NetTopologySuite, Version=1.12.4448.22555, Culture=neutral, PublicKeyToken=f580a05016ebada1' or one of its dependencies. The located assembly's manifest definition does not match the assembly reference. (Exception from HRESULT: 0x80131040)
       Source=Spatial4n.Core.NTS
       FileName=NetTopologySuite, Version=1.12.4448.22555, Culture=neutral, PublicKeyToken=f580a05016ebada1
       FusionLog==== Pre-bind state information ===
LOG: User = jpenka
LOG: DisplayName = NetTopologySuite, Version=1.12.4448.22555, Culture=neutral, PublicKeyToken=f580a05016ebada1
 (Fully-specified)
LOG: Appbase = file:///H:/Workspace/dotspatial-go2it/Build/Debug/
LOG: Initial PrivatePath = NULL
Calling assembly : Spatial4n.Core.NTS, Version=0.3.0.0, Culture=neutral, PublicKeyToken=9f9456e1ca16d45e.
===
LOG: This bind starts in default load context.
LOG: No application configuration file found.
LOG: Using host configuration file: 
LOG: Using machine configuration file from C:\Windows\Microsoft.NET\Framework\v4.0.30319\config\machine.config.
LOG: Post-policy reference: NetTopologySuite, Version=1.12.4448.22555, Culture=neutral, PublicKeyToken=f580a05016ebada1
LOG: Attempting download of new URL file:///H:/Workspace/dotspatial-go2it/Build/Debug/NetTopologySuite.DLL.
WRN: Comparing the assembly name resulted in the mismatch: Minor Version
ERR: Failed to complete setup of assembly (hr = 0x80131040). Probing terminated.

       StackTrace:
            at Spatial4n.Core.Context.Nts.NtsSpatialContext..ctor(Boolean geo)
            at Spatial4n.Core.Context.Nts.NtsSpatialContext..cctor() in z:\Projects\Spatial4n\Spatial4n.Core\Context\Nts\NtsSpatialContext.cs:line 40
       InnerException: 

~~~~