Revamp doc intro (#2588)

* Delete old stack diagram

* Update first paragraph

* Update introduction.rst

* Update introduction.rst

* Update introduction.rst

* Update introduction.rst

* Introduction graph optimization diagram

* Update introduction.rst

* Introduction kernel to deep learning frameworks

* Update introduction.rst

* Update introduction.rst

* Delete intro_kernel_to_fw.png

* Introduction kernel to frameworks with accent

* Update introduction.rst

* Update introduction.rst

* Update introduction.rst

* Introduction multiplying kernels

* Update introduction.rst

* Update introduction.rst

* Update introduction.rst

* Update introduction.rst

* Update introduction.rst

* Delete intro_kernel_to_fw_accent.png

* Introduction kernel explosion image

* Update introduction.rst

* Update introduction.rst

* Update introduction.rst

* Edit introduction to be relevant to a wider audience

* Refine intro

* writing thru another draft

* Another batch of updates

* Tie the conclusion to the intro

* Clean up the doc

* First reviewer feedback done!

* fix typo

* fix typos

* Minor formatting fixes

doc/sphinx/source/index.rst

@@ -48,6 +48,12 @@ nGraph Compiler stack
    core/passes/passes.rst
    buildlb.rst
    
+.. toctree::
+   :maxdepth: 1
+   :caption: Python API
+
+   python_api/index.rst
+
    
 .. toctree::
    :maxdepth: 1

doc/sphinx/source/project/about.rst

@@ -20,7 +20,7 @@ stack diagram is simplified to show how nGraph executes deep learning
 workloads with two hardware backends; however, many other deep learning
 frameworks and backends currently are functioning.
 
-.. figure:: ../graphics/stackngrknl.png
+.. figure:: ../graphics/stackngrknl-notice.png
    :alt: 
 
 Bridge

doc/sphinx/source/sitemap.rst

@@ -3,6 +3,6 @@
 .. _sitemap.rst:
  
 .. toctree::
-   :includehidden:
- 
+   :includehidden: 
+
    index.rst