memory docs (#1501)

docs/modules/memory/how_to_guides.rst

@@ -1,10 +1,23 @@
 How-To Guides
 =============
 
+Types
+-----
+
 The first set of examples all highlight different types of memory.
 
+`Buffer <./types/buffer.html>`_: How to use a type of memory that just keeps previous messages in a buffer.
+
+`Buffer Window <./types/buffer_window.html>`_: How to use a type of memory that keeps previous messages in a buffer but only uses the previous `k` of them.
+
+`Summary <./types/summary.html>`_: How to use a type of memory that summarizes previous messages.
+
+`Summary Buffer <./types/summary_buffer.html>`_: How to use a type of memory that keeps a buffer of messages up to a point, and then summarizes them.
+
 `Entity Memory <./types/entity_summary_memory.html>`_: How to use a type of memory that organizes information by entity.
 
+`Knowledge Graph Memory <./types/kg.html>`_: How to use a type of memory that extracts and organizes information in a knowledge graph
+
 
 .. toctree::
    :maxdepth: 1
@@ -13,6 +26,10 @@ The first set of examples all highlight different types of memory.
 
    ./types/*
 
+
+Usage
+-----
+
 The examples here all highlight how to use memory in different ways.
 
 `Adding Memory <./examples/adding_memory.html>`_: How to add a memory component to any single input chain.