Source Google Ads: Update docs

[artem1205]

What

Resolving https://github.com/airbytehq/oncall/issues/1279

How

Update docs

Pre-merge Checklist

Expand the relevant checklist and delete the others.

Updating a connector

Community member or Airbyter

• Grant edit access to maintainers (instructions)
• Secrets in the connector's spec are annotated with airbyte_secret
• Unit & integration tests added and passing. Community members, please provide proof of success locally e.g: screenshot or copy-paste unit, integration, and acceptance test output. To run acceptance tests for a Python connector, follow instructions in the README. For java connectors run ./gradlew :airbyte-integrations:connectors:<name>:integrationTest.
• Code reviews completed
• Documentation updated
  • Connector's README.md
  • Connector's bootstrap.md. See description and examples
  • Changelog updated in docs/integrations/<source or destination>/<name>.md including changelog. See changelog example
• PR name follows PR naming conventions

Airbyter

If this is a community PR, the Airbyte engineer reviewing this PR is responsible for the below items.

• Create a non-forked branch based on this PR and test the below items on it
• Build is successful
• If new credentials are required for use in CI, add them to GSM. Instructions.
• /test connector=connectors/<name> command is passing
• New Connector version released on Dockerhub and connector version bumped by running the /publish command described here