chore: set license in nuget package (#333)

Co-authored-by: Marco Studerus <[email protected]>

Author: e-i-n-s

src/OpenAI.csproj

@@ -5,6 +5,8 @@
     </Description>
     <AssemblyTitle>SDK Code Generation OpenAI</AssemblyTitle>
     <PackageTags>OpenAI;openai-dotnet;ChatGPT;Dall-E</PackageTags>
+    <PackageLicenseExpression>MIT</PackageLicenseExpression>
+    <Copyright>Copyright (c) 2024 OpenAI (https://openai.com)</Copyright>
 
     <VersionPrefix>2.2.0</VersionPrefix>
     <VersionSuffix>beta.2</VersionSuffix>