Update merge spmv readme

[jkinsky]

Existing Sample Changes

Description

Updated structure to match new template. Rewrote sections for clarity. Updated Windows information. Added missing sections and information.

Fixes Issue#

External Dependencies

N/A

Type of change

Please delete options that are not relevant. Add a 'X' to the one that is applicable.

• [x] Documentation

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [x] Command Line
• [x] oneapi-cli
• [x] Visual Studio
• [x] VSCode

[jkinsky]

@ishaghosh27 - please review. Adding @jimmytwei for notifcations.