Improve error msg on pip install dbt (#4244)

setup.py

@@ -6,10 +6,24 @@
 if 'sdist' not in sys.argv:
     print('')
     print('As of v1.0.0, `pip install dbt` is no longer supported.')
-    print('Instead, please use either:')
-    print('  - `pip install dbt-core`, for core functionality')
-    print('  - `pip install dbt-<adapter>`, to use dbt with your database, platform, or query engine')
-    print('See full list: https://docs.getdbt.com/docs/available-adapters')
+    print('Instead, please use one of the following.')
+    print('')
+    print('**To use dbt with your specific database, platform, or query engine:**')
+    print('')
+    print('    pip install dbt-<adapter>')
+    print('')
+    print('    See full list: https://docs.getdbt.com/docs/available-adapters')
+    print('')
+    print('**For developers of integrations with dbt Core:**')
+    print('')
+    print('    pip install dbt-core')
+    print('')
+    print('    Be advised, dbt Core''s python API is not yet stable or documented')
+    print('    (https://docs.getdbt.com/docs/running-a-dbt-project/dbt-api)')
+    print('')
+    print('**For the previous behavior of `pip install dbt`:**')
+    print('')
+    print('    pip install dbt-core dbt-postgres dbt-redshift dbt-snowflake dbt-bigquery')
     print('')
     sys.exit(1)