Add correct release notes and bring back net6 support

Author: synercoder

src/Directory.Build.props

@@ -2,7 +2,7 @@
 <Project>
 
   <PropertyGroup>
-    <TargetFrameworks>net8.0</TargetFrameworks>
+    <TargetFrameworks>net8.0;net6.0</TargetFrameworks>
     <MSBuildAllProjects>$(MSBuildAllProjects);$(MSBuildThisFileDirectory)..\Directory.Build.props</MSBuildAllProjects>
     <SynercodingProjectCategory>src</SynercodingProjectCategory>
   </PropertyGroup>

src/Synercoding.FileFormats.Pdf/PackageDetails.props

@@ -10,7 +10,7 @@
     <Product>Synercoding.FileFormats.Pdf</Product>
     <Title>Synercoding.FileFormats.Pdf</Title>
     <Description>Contains classes which makes it easy to quickly create a pdf file.</Description>
-    <PackageReleaseNotes>A fix with octal literal string encoding, and rewritten pdfname encoding, renamed art to artbox, and encoded artbox in resulting pdf.</PackageReleaseNotes>
+    <PackageReleaseNotes>Added transparent and separation images support. Content streams will be flatedecode encoded. And overprint mode support is added.</PackageReleaseNotes>
   </PropertyGroup>
 
 </Project>