Update README.md (#4)

Author: ploomiz

README.md

@@ -1,4 +1,38 @@
 # Eppo SDK for Python
 
+## Getting Started
+
+### Install and initialize the SDK client
+Install the package:
+```
+python3 -m pip install --upgrade eppo-server-sdk
+```
+
+Initialize the SDK with your Eppo API key:
+```
+import eppo_client
+from eppo_client import Config
+
+eppo_client.init(Config(api_key="<YOUR-API-KEY>"))
+```
+**The `init` method should be called once on applications startup**. The initialization method kicks off a polling process to retrieve experiment configurations from Eppo at regular intervals.
+
+### Use the client to assign variations
+Prerequisite: you must have configured an experiment in Eppo. To assign variations, your experiment should have a `RUNNING` status and a non-zero traffic allocation.
+
+Use the assignment API in any part of your code that needs to assign subjects to experiment variations:
+```
+import eppo_client
+
+client = eppo_client.get_instance()
+assigned_variation = client.assign("<subject>", "<experimentKey>")
+```
+
+The `subject` argument can be any entity identifier (e.g. a user ID). The experimentKey argument is the identifier of your Eppo experiment.
+
+The `assign` function will return null if the experiment is not running or if the subject is not part of the experiment traffic allocation.
+
+The `eppo_client.get_instance()` method returns a singleton client instance that is intended to be reused for the lifetime of your application.
+
 ## Supported Python Versions
-This version of the SDK is compatible with Python 3.6 and above.
+This version of the SDK is compatible with Python 3.6 and above.