Clarify 3.5 compatibility with 3.0 and 2.0

[mthalman]

Fixes #629

[MichaelSimons]

@richlander - Can you take a look at this change?

[MichaelSimons]

On one hand I like this proposal but on the other hand I feel like we are still not doing enough to clarify the versions supported by the 3.5 images. For example, they also support 4.8 apps. Would it make sense to add a column to the tag listing which lists which .NET versions are supported?

Windows Server, version 2004 amd64 Tags

Tag	Dockerfile	Supported .NET Versions
4.8-20200908-windowsservercore-2004, 4.8-windowsservercore-2004, 4.8, latest	Dockerfile	4.8
3.5-20200908-windowsservercore-2004, 4.8-3.5-20200908-windowsservercore-2004, 3.5-windowsservercore-2004, 4.8-3.5-windowsservercore-2004, 3.5	Dockerfile	4.8, 3.5, 3.0, 2.5

[mthalman]

On one hand I like this proposal but on the other hand I feel like we are still not doing enough to clarify the versions supported by the 3.5 images. For example, they also support 4.8 apps. Would it make sense to add a column to the tag listing which lists which .NET versions are supported?

I like that idea. In fact, doing that could prompt us to also remove the 4.8-3.5 tagging pattern.

[mthalman]

@MichaelSimons, @richlander -
I've added a compatibility matrix to help illustrate the full view of versions that are available. Let me know what you think.

[MichaelSimons]

I think this is a reasonable solution until MCR supports custom content in the tags table.

[MichaelSimons]

Suggested change

	\* The 4.8 SDK is also capable of building 4.8, 4.7.2, 4.7.1, 4.7, and 4.6.2 projects}}
	\* The 4.8 SDK is also capable of building 4.8, 4.7.2, 4.7.1, 4.7, and 4.6.2 projects.}}