chore (Badge) : Add .NET foundation badge

[ShreyasJejurkar]

1. Found the .NET foundation badge at https://img.shields.io/badge/.NET%20Foundation-blueviolet.svg
2. Add to badge collection.

[Pilchie]

@terrajobst - is this a thing other repos are doing?

[ShreyasJejurkar]

I have not seen this badge to other repo. But recently I cam across the new dotnet foundation project (https://github.com/reaqtive/reaqtor). And I saw that badge there!

[Pilchie]

@dotnet/aspdoi @dotnet/aspnet-build Any objections here? The site claims no tracking which was my only concern.

[dougbu]

Any objections here?

I can't see anything objectionable and we use https://shields.io/ badges already in the Readme file. We have the horizontal room for another badge, it looks pretty good, and the link is helpful (despite the license text at the top of most files).

Minor but how helpful is it is to add the badge w/o a dynamic label providing additional information❔ I can't think of a constraint we need to weigh against this but thought I'd ask.