update(readme): add example helm command line

[LucaGuerra]

What type of PR is this?

Uncomment one (or more) /kind <> lines:

/kind feature

/kind bug

/kind cleanup

/kind design

/kind documentation

/kind failing-test

Any specific area of the project related to this PR?

Uncomment one (or more) /area <> lines:

/area rules

/area registry

/area build

/area documentation

Proposed rule maturity level

Uncomment one (or more) /area <> lines (only for PRs that add or modify rules):

/area maturity-stable

/area maturity-incubating

/area maturity-sandbox

/area maturity-deprecated

What this PR does / why we need it:

I believe it would be beneficial to users to understand how to enable all the rules present in this repository. The alternative is to add this example command line to the Helm repo (as well?)

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

[poiana]

LGTM label has been added.

Git tree hash: 4a0547781c02f7296f01d2fd6f47b64f896f5643

[poiana]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: FedeDP, LucaGuerra

The full list of commands accepted by this bot can be found here.

The pull request process is described here

Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/falcosecurity/rules/blob/main/OWNERS)~~ [FedeDP,LucaGuerra] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment