Add NuGet.config

Dockerfile

@@ -3,6 +3,7 @@ FROM mcr.microsoft.com/dotnet/sdk:5.0 AS build
 WORKDIR /src
 
 COPY favicon.ico ./
+COPY NuGet.config ./
 COPY Directory.Build.props ./
 COPY DiscordChatExporter.Core DiscordChatExporter.Core
 COPY DiscordChatExporter.Cli DiscordChatExporter.Cli

NuGet.config

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<configuration>
+  <packageSources>
+    <clear />
+    <add key="nuget" value="https://api.nuget.org/v3/index.json" />
+  </packageSources>
+</configuration>