Need to update menu-item instruction for Optional Packages as per v6

[karandatwani92]

Solves https://github.com/Laravel-Backpack/LogManager/issues/64

v6 menu command added

[welcome[bot]]

BOOM! Your first PR with us, thank you so much! Someone will take a look at it shortly. Please keep in mind that:

• if this constitutes a breaking change, it might take quite a while for this to get merged; we try to emulate the Laravel release cycle as much as possible, so developers can upgrade both software once; this means a new big release every ~6 months;
• even if it's a non-breaking change, it might take a few days/weeks for the PR to get merged; unless it's a no-brainer, we like to have some community feedback on new features, before we merge them; this leads to higher-quality code, in the end; we learnt this the hard way :-)
• not all PRs get merged; sometimes we just have to hold out new features, to keep the packages lean; sometimes we don't include features that only apply to niche use cases;
• we're not perfect; if you think we're wrong, call us out on it; but in a kind way :-) we all make mistakes, best we learn from them and build better software together;

Thank you! -- Justin Case The Backpack Robot

[welcome[bot]]

WHOOP-WHOOP! Congrats, your first PR on this repo has officialy been merged. If you want to help out the community in other ways, you can:

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