Update index.md with brew trust call for newer versions of brew

[anthonycorletti]

Add a trust call for newer versions of brew https://docs.brew.sh/Tap-Trust.

Just tapping and installing without trusting on newer versions of brew causes the following error.

brew install datumctl
Error: Refusing to load formula datum-cloud/tap/datumctl from untrusted tap datum-cloud/tap.
Run `brew trust --formula datum-cloud/tap/datumctl` or `brew trust datum-cloud/tap` to trust it.

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[cla-assistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}