[Docs/Contributing] Clarify "target" variable usage in Makefile (adapter selection)

[nijanthanvijayakumar]

Explanation

When following the “Setting up an environment” section of the CONTRIBUTING.md, the instructions suggest using make dev.

However, the Makefile is currently written with a target variable that controls which adapter to install. For example, to install dbt-postgres, the correct command is:

make dev target=postgres

Without specifying target, the Makefile defaults to running:

pip install --pre "dbt-"

which fails with:

ERROR: Invalid requirement: 'dbt-'

This behaviour would be confusing for contributors (particularly the new ones) because the documentation never mentions that:

1. target corresponds to the adapter name
2. The available adapters are already listed in dev-requirements.txt:
   • dbt-postgres
   • dbt-redshift
   • dbt-core
   • dbt-bigquery
   • dot-snowflake

Suggested Improvement

The CONTRIBUTING.md should explicitly mention:

• That make dev requires a target argument to specify the adapter.
• A simple usage example, e.g.:

make dev target=postgres

• A note pointing contributors to dev-requirements.txt for the full list of supported adapters.

This small clarification would prevent the installation error and make the contributor onboarding experience much smoother.