Add NuGet installation readme

Author: rasmusjp

src/Our.Umbraco.GraphQL/Our.Umbraco.GraphQL.csproj

@@ -20,6 +20,7 @@
 
     <ItemGroup>
         <None Include="content\**" Pack="True" PackagePath="content\" />
+        <None Include="readme.txt" Pack="True" PackagePath="" />
     </ItemGroup>
 
     <ItemGroup>

src/Our.Umbraco.GraphQL/readme.txt

@@ -0,0 +1,15 @@
+ _____                 _     _____ _        __             _   _           _                         
+|  __ \               | |   |  _  | |      / _|           | | | |         | |                        
+| |  \/_ __ __ _ _ __ | |__ | | | | |     | |_ ___  _ __  | | | |_ __ ___ | |__  _ __ __ _  ___ ___  
+| | __| '__/ _` | '_ \| '_ \| | | | |     |  _/ _ \| '__| | | | | '_ ` _ \| '_ \| '__/ _` |/ __/ _ \ 
+| |_\ \ | | (_| | |_) | | | \ \/' / |____ | || (_) | |    | |_| | | | | | | |_) | | | (_| | (_| (_) |
+ \____/_|  \__,_| .__/|_| |_|\_/\_\_____/ |_| \___/|_|     \___/|_| |_| |_|_.__/|_|  \__,_|\___\___/ 
+                | |                                                                                  
+                |_|                                                                                  
+
+This package currently is intended for development-level testing right now.
+
+All doctypes and media properties are accessible via the GraphQL endpoint by anyone, as permissions and other security features aren't yet present.
+Don't use this on any data you need to keep protected
+
+For more info visit https://github.com/rasmusjp/umbraco-graphql/