Update with `softrvv` workflow

Softrvv workflow is very different from the prior, with much fewer
lines of code entailed when adding a new op to test-suite.

This also includes documentation around using the team's tracker/sign-up
spreadsheet for the different vector-op-unit-tests.

Change-Id: I4afc3d768080bcffd7b8484643ddf12cbbb3c12f