Small changes to compatibility for .NET

[papafe]

I did some small changes:

• Made explicit we support .NET 5.0 and older versions. Strictly speaking .NET Core 2.0 and later includes .NET 5.0 but because the naming on .NET is very confusing, I think it makes sense to make it clear
• Ordered the top part, so that iOS and MacOS sections are close, same for iOS and Android+
• Removed the word "framework". The thing is that there is already .NET Framework, so the word framework here could be confusing... I could be convinced it makes sense though 😁
• Modified a little the windows section so it seems slightly more consistent

[github-actions]

Readability for Commit Hash: 550765f

You can see any previous Readability scores (if they exist) by looking
at the comment's history.

Flesch Reading Ease scores for changed documents:

• source/sdk/dotnet/compatibility: 61.63

The following table can be helpful in assessing the readability score of a document.

Score	Difficulty
90-100	Very Easy
80-89	Easy
70-79	Fairly Easy
60-69	Medium
50-59	Fairly Hard
30-49	Hard
0-29	Very Hard

[MongoCaleb]

@papafe can you please rebase from upstream/master? That should fix the build errors.

[papafe]

@MongoCaleb Sure, I've just done it