Update commcare.md

[AishaHassen]

Short Description

This PR adds a section on tips of how to use CommCare Lookup tables, which APIs to use and when

Details

This PR covers some of our learnings during the ASRI Commcare-satusehat project around lookup tables.

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[aleksa-krolls]

@AishaHassen nice! Only change I'd suggest is linking to the CommCare docs about (1) lookup tables feature and (2) lookup API docs

[aleksa-krolls]

Please just add links to the commcare docs!