Update README.rst (open-telemetry#2575)

Author: lzchen

processor/opentelemetry-processor-baggage/README.rst

@@ -1,10 +1,22 @@
 OpenTelemetry Baggage Span Processor
 ====================================
 
+|pypi|
+
+.. |pypi| image:: https://badge.fury.io/py/opentelemetry-processor-baggage.svg
+   :target: https://pypi.org/project/opentelemetry-processor-baggage/
+
 The BaggageSpanProcessor reads entries stored in Baggage
 from the parent context and adds the baggage entries' keys and
 values to the span as attributes on span start.
 
+Installation
+------------
+
+::
+
+    pip install opentelemetry-processor-baggage
+
 Add this span processor to a tracer provider.
 
 Keys and values added to Baggage will appear on subsequent child
@@ -48,4 +60,4 @@ For example, to only copy baggage entries that match the regex `^key.+`:
 ```python
 regex_predicate = lambda baggage_key: baggage_key.startswith("^key.+")
 tracer_provider.add_span_processor(BaggageSpanProcessor(regex_predicate))
-```
+```