[DOC] Clarify vex output cannot be generated with update all

[ashnamehrotra]

What kind of documentation improvement is needed?

None

What is the change that is needed?

Clarify Copa will not be able to provide any vex output with upgrade all approach since it doesn't have any info on CVEs associated with the package upgrades in https://project-copacetic.github.io/copacetic/website/output

Are you willing to submit PRs to contribute to documentation?

• [ ] Yes, I am willing to implement it.

[Nishant-k-sagar]

Hey @ashnamehrotra, I have gone through the codebase structure in this repo, and can improve documentation, can you assign me this documentation update/change issue, and tell or guide me what specific output will you like to add in output.md

[ashnamehrotra]

@Nishant-k-sagar assigned, thanks! we just want to clarify that the vex output is only possible if using the patching approach with scan report