Fix package issues (#61)

Author: VisualMelon

Icons/OxyPlot_128.png

@@ -22,6 +22,9 @@ To use the library, add the following to your `App.xaml`:
 
         <!-- Add the line below to get OxyPlot UI theme applied. -->
         <StyleInclude Source="resm:OxyPlot.Avalonia.Themes.Default.xaml?assembly=OxyPlot.Avalonia"/>
+      
+        <!-- Add the line below to get OxyPlot UI theme applied in Avalonia 11. -->
+        <StyleInclude Source="avares://AvaloniaEdit/Themes/Simple/AvaloniaEdit.xaml"/>
     </Application.Styles>
 </Application>
 ```

README.md

@@ -7,14 +7,20 @@
     <PackageLicenseExpression>MIT</PackageLicenseExpression>
     <Copyright>OxyPlot contributors</Copyright>
     <PackageProjectUrl>http://oxyplot.org/</PackageProjectUrl>
-    <PackageIconUrl>https://raw.githubusercontent.com/oxyplot/oxyplot/develop/Icons/OxyPlot_128.png</PackageIconUrl>
+    <PackageIcon>OxyPlot_128.png</PackageIcon>
+    <PackageReadmeFile>README.md</PackageReadmeFile>
     <PackageTags>plotting plot charting chart</PackageTags>
     <RepositoryType>git</RepositoryType>
     <RepositoryUrl>https://github.com/oxyplot/oxyplot.git</RepositoryUrl>
     <VersionPrefix>2.1.2</VersionPrefix>
     <LangVersion>latest</LangVersion>
   </PropertyGroup>
 
+  <ItemGroup Condition="$(GeneratePackageOnBuild)">
+    <None Include="$(MSBuildThisFileDirectory)../../Icons/OxyPlot_128.png" Pack="true" PackagePath="\" Visible="false" />
+    <None Include="$(MSBuildThisFileDirectory)../../README.md" Pack="true" PackagePath="\" Visible="false" />
+  </ItemGroup>
+
   <ItemGroup>
     <Compile Update="**\*.xaml.cs">
       <DependentUpon>%(Filename)</DependentUpon>