adding CLI release notes

[anaxceron]

Describe your pull request here: Adding Zowe CLI release notes for Zowe v3.1 release

List the file(s) included in this PR: docs\whats-new\release-notes\v3_1_0.md

After creating the PR, follow the instructions in the comments.

[github-actions]

😺 Thank you for creating this PR! To publish your content to Zowe Docs, follow these steps.

• Add the label review: sme if an SME needs to check your content.
• Identify your content topic with a label. (Examples: area: apiml, area: cli, area: install and config, etc.)
• Specify the major Zowe release(s) for your content. (Examples: release: V1, release: V2, release: V3)
  • If adding content that needs to be removed from V3 documentation, add the V3 N/A tag.
• Link any Doc Issues related to this PR.
• Fix broken links found in your content areas.
• Notify the SME to review this PR (if applicable).
• Merge to the master branch if your PR updates content that is on the live site. Merge to docs-staging if your PR updates content for a future release.

[github-actions]

😺 Thank you for creating this PR! To publish your content to Zowe Docs, follow these steps.

• Add the label review: sme if an SME needs to check your content.
• Identify your content topic with a label. (Examples: area: apiml, area: cli, area: install and config, etc.)
• Specify the major Zowe release(s) for your content. (Examples: release: V1, release: V2, release: V3)
  • If adding content that needs to be removed from V3 documentation, add the V3 N/A tag.
• Link any Doc Issues related to this PR.
• Fix broken links found in your content areas.
• Notify the SME to review this PR (if applicable).
• Merge to the master branch if your PR updates content that is on the live site. Merge to docs-staging if your PR updates content for a future release.

[github-actions]

🚀 Deployed on https://67890adf8e7c501870c7b67e--zowe-docs-master.netlify.app

[adam-wolfe]

LGTM, thanks @anaxceron