cleanup windows install docs

What does this MR do?

• Add missing steps to Windows install details

• Use gitlab-runner rather than gitlab-ci-multi-runner.exe in support of https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/issues/1195

• Document how to use with true service account (Built-in System Account)

• General cleanup

• Provide better link on how to run elevated command prompt

Replaces https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/482 & https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/492 & https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/493

mentioned in merge request !493 (closed)

@axil can I get a review and merge? I addressed the comment you left in https://gitlab.com/gitlab-org/gitlab-ci-multi-runner/merge_requests/493.

added 1 commit

• a924e773 - add concurrent job details

Compare with previous version

Great! Thanks @bbodenmiller

added ~60197 osWindows labels

changed milestone to %v9.0

assigned to @axil

merged

mentioned in issue #2277 (closed)

added Documentation and removed ~60197 labels