Add correction to Decision: Batching Strategy section in index.md

[danghle]

A more frequent batching strategy implies fewer conversions which implies less signal to noise, a fact that is reiterated in the documents linked at the end of this section.

[chrome-devrel-infra[bot]]

:white_check_mark: Preview (static) for commit 7a5470219315f5c270b087aedfd6dbf99c8075a3 available at https://pr-7339-static-dot-dcc-staging.uc.r.appspot.com/.

The following pages likely changed with this PR:

• https://pr-7339-static-dot-dcc-staging.uc.r.appspot.com/docs/privacy-sandbox/summary-reports/design-decisions/

[samdutton]

Hi @maudnals — I know you're not working on ARA now, but would you be able to review this one word change? Thanks.