Add Python version support policy (open-telemetry#2397)

* Add Python version support policy

Fixes open-telemetry#2395

* Address comments

* Fix a mistake

Author: ocelotl

CHANGELOG.md

@@ -9,6 +9,8 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Fix SpanLimits global span limit defaulting when set to 0
   ([#2398](https://github.com/open-telemetry/opentelemetry-python/pull/2398))
+- Add Python version support policy
+  ([#2397](https://github.com/open-telemetry/opentelemetry-python/pull/2397))
 - Decode URL-encoded headers in environment variables
   ([#2312](https://github.com/open-telemetry/opentelemetry-python/pull/2312))
 - [exporter/opentelemetry-exporter-otlp-proto-grpc] Add OTLPMetricExporter

README.md

@@ -110,6 +110,14 @@ pip install scalene
 scalene opentelemetry-<PACKAGE>/tests/performance/resource-usage/<PATH_TO_TEST>/profile_resource_usage_<NAME_OF_TEST>.py
 ```
 
+## Python Version Support Addition and Removal
+
+This project supports the latest Python versions. As new Python versions are released, support for them is added and
+as old Python versions reach their end of life, support for them is removed.
+
+We add support for new Python versions no later than 3 months after they become stable.
+
+We remove support for old Python versions 6 months after they reach their [end of life](https://devguide.python.org/devcycle/#end-of-life-branches).
 
 ## Documentation