More documentation about custom actions

[fabiosantoscode]

Describe the problem feature solves I'm currently trying to implement a custom bulk action and I found some places that weren't documented enough

Describe the solution you'd like

• the ./path-to-component example as an argument to AdminJS.bundle() should mention where "." is. In retrospect it's probably CWD and not resolved like a require() but I ended up using __dirname after a few attempts.
• The documentation should provide at least one example of implementing a component for a custom action (using its props), and maybe components for other things.

Describe alternatives you've considered I ended up using a lot of console.log, reading the source and guessing things.

Acceptance criteria Described "solution you'd like"

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I'm open to pushing a PR to the documentation so let me know if you'd like me to.