Update README.md (#14432)

Add minimum version number to PostgreSQL in 'Getting Started,' to help potential contributors successfully set up environment with local database.

I tried to set up local dev environment on Ubuntu 20.04 with PostgreSQL 12.18 which failed when running 'yarn workspace @calcom/prisma db-migrate'

PostgreSQL version 14.11 worked for me. I saw another dev say v. 13+ would work. Could save folks some troubleshooting time.

This is the error on PostgreSQL 12.18:

Error: P3006 Migration `20240321143215_move_avatars_cols_to_avatar_table` failed to apply cleanly to the shadow database. Error: ERROR: function gen_random_uuid() does not exist HINT: No function matches the given name and argument types. You might need to add explicit type casts. 0: sql_schema_connector::validate_migrations with namespaces=None at schema-engine/connectors/sql-schema-connector/src/lib.rs:324 1: schema_core::state::DevDiagnostic at schema-engine/core/src/state.rs:270

README.md

@@ -113,7 +113,7 @@ To get a local copy up and running, please follow these simple steps.
 Here is what you need to be able to run Cal.com.
 
 - Node.js (Version: >=18.x)
-- PostgreSQL
+- PostgreSQL (Version: >=13.x)
 - Yarn _(recommended)_
 
 > If you want to enable any of the available integrations, you may want to obtain additional credentials for each one. More details on this can be found below under the [integrations section](#integrations).