Add nuget package badge and link

[WeihanLi]

**Closes #148 **

Preview here: https://github.com/WeihanLi/dotnet-CommunityTookit/blob/nuget-package-enhancement/README.md

Add the NuGet package badge and link to the NuGet package, hope it would help developers find the NuGet packages more easily

PR Checklist

• Created a feature/dev branch in your fork (vs. submitting directly from a commit on main)
• Based off latest main branch of toolkit
• PR doesn't include merge commits (always rebase on top of our main, if needed)
• Tested code with current supported SDKs
• New component
  • Pull Request has been submitted to the documentation repository instructions. Link:
  • Added description of major feature to project description for NuGet package (4000 total character limit, so don't push entire description over that)
• Tests for the changes have been added (for bug fixes / features) (if applicable)
• Header has been added to all new source files (run build/UpdateHeaders.bat)
• Contains NO breaking changes
• Every new API (including internal ones) has full XML docs
• Code follows all style conventions

Other information

[Nirmal4G]

A table format should be a better choice instead of in-lining the badges. They also look mis-aligned!

[WeihanLi]

Would it looks better likes follows, maybe need a new block for the table:

Package	Latest stable	Latest Preview
CommunityToolkit.Mvvm
CommunityToolkit.Diagnostics
CommunityToolkit.HighPerformance
CommunityToolkit.Common

[Nirmal4G]

This looks nice but add the help links to the package name column and add a description column at the end. Like this.

Package	Latest Stable	Latest Preview	Description
CommunityToolkit.Common			This library has a set of helper APIs, shared with other CommunityToolkit libraries.

[WeihanLi]

@Nirmal4G updated with table, looks better, thanks

[hawkerm]

Thoughts on updating the upper-right package link to?

I think it's pointing to 7.1.2 as it's pointing to Microsoft.Toolkit as the profile for the owner on NuGet and getting confused with the package for the same name?

[Nirmal4G]

If we do that, then we should display both Microsoft.Toolkit.* and CommunityToolkit.* packages until we migrate away from the former packages.

@Sergio0694 and @michael-hawker Thoughts?

[Sergio0694]

"until we migrate away from the former packages"

Not sure what you mean, we've already migrated away. I literally deprecated the Microsoft.Toolkit.* packages on NuGet 🙂

[Nirmal4G]

I should have mentioned that "we" is "Community"! Sorry about that. But if it's not needed to display older packages, then we can remove it! Just wanted to be sure!! 😇

[Nirmal4G]

PR #439 should merge first. It might break this. So, don't forget to use the updated URLs and rebase on top of that merge.

[MisinformedDNA]

So we need the source generator package listed given it's not a package?

[Sergio0694]

No, it should not be listed, it was my mistake adding that initially. It's just not a package, it should not be there 🙂

[WeihanLi]

Close it for a clean commit PR

[Nirmal4G]

You could've just force-pushed!? Anyways it's fine.