Detailed guidelines end-to-end for source-build

[ashnaga]

No description provided.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this PR. If you have write-permissions please help me learn by adding exactly one area label.

[ashnaga]

Need input in bootstrapping-guidelines for the following -

1. Arguments to be passed in the commands marked as - (args???)

2. How to update the RID graph - [UPDATE THE RID GRAPH???]

3. If no compatible OS/platform found
   In stage 1, create portable SDK (this step works for .NET 6, but not for .NET 7). [Define the steps in here???]

4. Building for New Architecture (Unsupported)
   [Define the recommended process and add the steps in this section???]

[MichaelSimons]

I pushed a few updates to correct syntax issues. Consider utilizing a linter to catch these. I like using VSCode with a markdown linter extension.

[MichaelSimons]

I pushed some updates to the system-requirements in an attempt to make the doc easier to scan and pick up pertinent info.

[MichaelSimons]

FYI - I pushed some changes to simplify and re-order a few things. This is ready for review.