#6 Implement Broadcasts.get_players

[nstillman-te]

Part of #6.

Implements GET /broadcast/{broadcastTournamentId}/players as client.broadcasts.get_players. Adds BroadcastTournamentPlayer TypedDict, VCR test, and README.rst / CHANGELOG.rst updates.

Checklist when adding a new endpoint

• Added new endpoint to the README.rst
• Ensured that my endpoint name does not repeat the name of the client. Wrong: client.users.get_user(), Correct: client.users.get()
• Typed the returned JSON using TypedDicts in berserk/types/, example
• Written tests for GET endpoints not requiring authentification. Documentation, example
• Added the endpoint to CHANGELOG.rst in the To be released section (to be created if necessary)