Include information about nuget.config in .NET Core documentation (#1072)

* Add information about nuget.config to .NET Core

Add information about how to include a nuget.config in a .NET Core function

* Make information about nuget.config more concise

Author: GGG-KILLER

docs/runtimes.md

@@ -436,6 +436,14 @@ You can deploy them using the command:
 kubeless function deploy fibonacci --from-file fibonacci.cs --handler module.handler --dependencies fibonacci.csproj --runtime dotnetcore2.0
 ```
 
+##### `nuget.config`
+
+If you happen to be using custom nuget repositories through a `nuget.config` file, you'll need to include the file along with the code inside a `.zip` file and then you can deploy the function with the `nuget.config` using the command:
+
+```bash
+kubeless function deploy custom-deps --from-file custom-deps.zip --handler module.handler --dependencies custom-deps.csproj --runtime dotnetcore2.0
+```
+
 ### Ballerina
 
 #### Example