pw_protobuf: expand docs
This change updates the protobuf docs to explain the module's design
decisions.
Change-Id: Idccacf28651cf091218dabb1d1ad09365d445776
diff --git a/pw_protobuf/decoding.rst b/pw_protobuf/decoding.rst
new file mode 100644
index 0000000..7c75a2e
--- /dev/null
+++ b/pw_protobuf/decoding.rst
@@ -0,0 +1,31 @@
+.. default-domain:: cpp
+
+.. highlight:: sh
+
+.. _chapter-protobuf-decoder:
+
+--------
+Decoding
+--------
+
+Size report
+===========
+
+Full size report
+^^^^^^^^^^^^^^^^
+
+This report demonstrates the size of using the entire decoder with all of its
+decode methods and a decode callback for a proto message containing each of the
+protobuf field types.
+
+.. include:: size_report/decoder_full.rst
+
+
+Incremental size report
+^^^^^^^^^^^^^^^^^^^^^^^
+
+This report is generated using the full report as a base and adding some int32
+fields to the decode callback to demonstrate the incremental cost of decoding
+fields in a message.
+
+.. include:: size_report/decoder_incremental.rst