pip install xee now supported.

This PR updates our documentation to instruct users to install `Xee` from PyPI. I've also added an extra step in the README walkthrough (imports).

Fixes #27.

PiperOrigin-RevId: 572361717

README.md

@@ -8,10 +8,10 @@ _An Xarray extension for Google Earth Engine._
 
 ## How to use
 
-Install with pip (distributions on PyPi will come soon):
+Install with pip:
 
 ```shell
-pip install git+https://github.com/google/xee.git
+pip install --upgrade xee
 ```
 
 Then, authenticate Earth Engine:
@@ -20,6 +20,13 @@ Then, authenticate Earth Engine:
 earthengine authenticate --quiet
 ```
 
+Now, in your Python environment, make the following imports:
+
+```python
+import ee
+import xarray
+```
+
 Next, initialize the EE client with the high volume API:
 
 ```python