fix: update README with the correct node version (v18)

[OrRosenblatt]

Fixes

Update the README.md documentation with the correct node version (v18), following the latest releases of twilio-cli & twilio-cli-core that bumped the supported node version to v18 from v14 (PRs: #537, #540 & twilio/twilio-cli-core#226).

Checklist

• I acknowledge that all my contributions will be made under the project's license
• I have made a material change to the repo (functionality, testing, spelling, grammar)
• I have read the Contribution Guidelines and my PR follows them
• I have titled the PR appropriately
• I have updated my branch with the main branch
• I have added tests that prove my fix is effective or that my feature works
• I have added the necessary documentation about the functionality in the appropriate .md file
• I have added inline documentation to the code I modified

If you have questions, please file a support ticket, or create a GitHub Issue in this repository.

[AsabuHere]

LGTM

The docker container & oclif workflow now uses node v18 to build itself. But that doesn't mean we support node v18+ only. We only package using node v18.

[OrRosenblatt]

The docker container & oclif workflow now uses node v18 to build itself. But that doesn't mean we support node v18+ only. We only package using node v18.

@AsabuHere The documentation is not about supporting only node v18+, but on top of supporting node v16 & node v14. Can you please help me understand - which node versions the Twilio CLI support? node10.x? node12.x? node14.x? node16.x? node18.x? node20.x? All of the above? only certain versions?