Cleaned metadata & added install from Package Manager notes

[JamesMcGhee]

• Cleaned up the metadata removing 2 un-used ones and adding in the 2 missing ones
• Updated the Readme.md to instruct on install from Package Manager

This would resolve the issue reported in #454 and the sugestion in #449

[JamesMcGhee]

For those looking for it now

You can install from package manager off this fork via

https://github.com/JamesMcGhee/Steamworks.NET.git?path=/com.rlabrecque.steamworks.net

[rlabrecque]

Merged, though we really need to clarify that the package manager version is completely missing the default user implementation of SteamManager, probably doesn't matter for you guys, but will matter for most people.

[JamesMcGhee]

Just saw this

SteamManager would be best served I think as a Sample
This can then be optionally downloaded after install of the Steamworks.NET forom the Package Mangaer by simply clicking a link on it ... we do this with our System Core kit

This way SteamManager isn't in by default as in most cases really it shouldn't be

The up side to doing it as a sample is when its sample code its in the project proper so they can modify it

More to the point I think SteamManager fills a need for new users but also causes some issues with regards to 3rd parties using it not just us but also for example transports to various HLAPI like Mirror, Mirrage, MLAPI, etc.

I'll see if I can get some time to create a full on sample scene with "a" steam initalization script set up as simply as possible. I think the objective should be to teach people how to make there own as opposed to perscribe a given Steam Manager as that will always conflcit with 3rd parties to some extent ... or shoe horn them into whatever design decisions where made in that perscribed manager which has been an issue with Steam Manager in the past.