add readme for nuget & fix warning

Author: doghappy

src/SocketIOClient.Serializer.NewtonsoftJson/NewtonJsonAckMessage.cs

@@ -10,7 +10,7 @@ public class NewtonJsonAckMessage : INewtonJsonAckMessage
     public JArray DataItems { get; set; } = null!;
 
     public virtual MessageType Type => MessageType.Ack;
-    public string Namespace { get; set; } = null!;
+    public string? Namespace { get; set; }
     public int Id { get; set; }
     public string RawText { get; set; } = null!;
     public JsonSerializerSettings JsonSerializerSettings { get; set; } = null!;

src/SocketIOClient.Serializer.NewtonsoftJson/NewtonJsonEngineIO3MessageAdapter.cs

@@ -18,7 +18,7 @@ public ConnectedMessage DeserializeConnectedMessage(string text)
 
     public ErrorMessage DeserializeErrorMessage(string text)
     {
-        var error = JToken.Parse(text).ToObject<string>();
+        var error = JToken.Parse(text).ToObject<string>()!;
         return new ErrorMessage
         {
             Error = error,

src/SocketIOClient.Serializer.NewtonsoftJson/NewtonJsonEngineIO4MessageAdapter.cs

@@ -29,7 +29,7 @@ public ErrorMessage DeserializeErrorMessage(string text)
     {
         var message = new ErrorMessage();
         var rawJson = DecapsulateNamespace(text, message);
-        message.Error = JObject.Parse(rawJson).Value<string>("message");
+        message.Error = JObject.Parse(rawJson).Value<string>("message")!;
         return message;
     }
 }

src/SocketIOClient.Serializer.NewtonsoftJson/NewtonJsonSerializer.cs

@@ -88,7 +88,7 @@ private static void SetEventMessageProperties(
         JsonSerializerSettings settings)
     {
         SetAckMessageProperties(result, message, settings);
-        message.Event = message.DataItems[0].Value<string>();
+        message.Event = message.DataItems[0].Value<string>()!;
         message.DataItems.RemoveAt(0);
     }
 

src/SocketIOClient/SocketIOClient.csproj

@@ -10,6 +10,7 @@
         <RepositoryUrl>https://github.com/doghappy/socket.io-client-csharp</RepositoryUrl>
         <PackageRequireLicenseAcceptance>false</PackageRequireLicenseAcceptance>
         <PackageTags>socket.io-client</PackageTags>
+        <PackageReadmeFile>README.md</PackageReadmeFile>
         <RepositoryType>github</RepositoryType>
         <Version>4.0.0</Version>
         <PackageLicenseExpression>MIT</PackageLicenseExpression>
@@ -27,6 +28,8 @@
         <ProjectReference Include="..\SocketIOClient.Common\SocketIOClient.Common.csproj" />
         <ProjectReference Include="..\SocketIOClient.Serializer.NewtonsoftJson\SocketIOClient.Serializer.NewtonsoftJson.csproj"/>
         <ProjectReference Include="..\SocketIOClient.Serializer\SocketIOClient.Serializer.csproj"/>
+        <None Include="..\..\README.md" Pack="true" PackagePath="\"/>
+        <None Include="..\..\README.zh.md" Pack="true" PackagePath="\"/>
     </ItemGroup>
 
     <ItemGroup>