docs: add command to run acceptance tests (#5025)

CONTRIBUTING.md

@@ -105,6 +105,12 @@ Use [fake-server](./test/acceptance/fake-server.ts) to mock any Snyk API calls.
 
 Place fixtures in `./test/fixtures`. Keep them minimal to reduce maintenance. Use [`createProject`](./test/jest/util/createProject.ts) to use your fixtures in isolated working directories for your tests.
 
+You can run acceptance tests with:
+
+```
+npm run test:acceptance -- --selectProjects snyk
+```
+
 ### Smoke Tests
 
 Smoke tests typically don't run on branches unless the branch is specifically prefixed with `smoke/`. They usually run on an hourly basis against the latest published version of the CLI.