Update 'Client'

Client.md

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+# PythonRMV Client
+You are now viewing the main class of the module, its heart. The main Client class, all available normal methods can be found here.  
+
+This page is about the Client class, which exposes high-level methods for an easy access to the API.
+
+```py
+from pyrmv import Client
+
+client = Client("SampleAPIKey")
+
+print(client.stop_by_id("A=1@O=Offenbach (Main)-Zentrum Marktplatz\/Frankf. Straße@X=8764456@Y=50105181@U=80@L=3002510@"))
+```
+
+# Details
+
+## `class pyrmv.Client`
+
+### Parameters
+* access_key (`str`) – Access ID for identifying the requesting client. Get your key on [RMV website](https://opendata.rmv.de/site/start.html).
+
+### Methods:
+* board_arrival -> `BoardArrival`
+* board_departure -> `BoardDeparture`
+* him_search -> `List[Message]`
+* journey_detail -> `Journey`
+* stop_by_coords -> `List[Stop]`
+* stop_by_id -> `Union[Stop, None]`
+* stop_by_name -> `List[Stop]`
+* trip_find -> `List[Trip]`
+* trip_recon -> `List[Trip]`