add a short doc on releasing

[jtoar]

why

releasing is scary, but everyone working on stagehand should feel empowered to do it

what changed

we will add more github workflows to automate the process, but this PR starts small by adding a short doc on how to do a release manually from the CLI

test plan

i've been testing on my fork

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[kamath]

thanks for this @jtoar! 🐐