Wiki: Add AspNetCore package to installation docs

[tdbrian]

Bummer I can't submit a PR to the wiki because of how it works on GitHub, but I pushed my own fork with the addition here.

https://github.com/tdbrian/PlatibusWiki/blob/master/1.-Installation.md#platibusaspnetcore

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Platibus.AspNetCore

AspNetCore support is provided in the Platibus.AspNetCore package. This package allows for configuration through ConfigurePlatibus on the IServiceCollection and middleware setup through UsePlatibusMiddleware on the IApplicationBuilder. This library provides a .Net Core logging sink as well.

To install, search for and install the package Platibus.AspNetCore in the NuGet package manager or run the following PowerShell command from the NuGet Package Manager Console:

PM> Install-Package Platibus.AspNetCore