[OV2.0] Preprocessing documentation (openvinotoolkit#10451)

* [OV2.0] Preprocessing documentation - first draft

* Small update

* Added ov::Layout overview

* Fix code style

* Preprocessing details - ~50% done

* Corrected links

* Fixed comments, added more docs

* Minor updates

* Couple more links

* Fixed comments

* Remove 'future' link

docs/OV_Runtime_UG/OpenVINO_Runtime_User_Guide.md

@@ -10,6 +10,7 @@
 
    openvino_docs_IE_DG_Integrate_with_customer_application_new_API
    openvino_docs_OV_Runtime_UG_Model_Representation
+   openvino_docs_OV_Runtime_UG_Preprocessing_Overview
    <!-- rename to "Changing input shapes" -->
    openvino_docs_IE_DG_ShapeInference
    openvino_docs_IE_DG_Device_Plugins

docs/OV_Runtime_UG/layout_overview.md

@@ -0,0 +1,154 @@
+# Layout API overview {#openvino_docs_OV_Runtime_UG_Layout_Overview}
+
+## Introduction
+
+In few words, with layout `NCHW` it is easier to understand what model's shape `{8, 3, 224, 224}` means. Without layout it is just a 4-dimensional tensor.
+
+
+Concept of layout helps you (and your application) to understand what does each particular dimension of input/output tensor mean. For example, if your input has shape `{1, 3, 720, 1280}` and layout "NCHW" - it is clear that `N(batch) = 1`, `C(channels) = 3`, `H(height) = 720` and `W(width) = 1280`. Without layout information `{1, 3, 720, 1280}` doesn't give any idea to your application what these number mean and how to resize input image to fit model's expectations.
+
+
+Reasons when you may want to care about input/output layout:
+ - Perform model modification:
+    - Apply [preprocessing](./preprocessing_overview.md) steps, like subtract means, divide by scales, resize image, convert RGB<->BGR
+    - Set/get batch for a model
+ - Same operations, used during model conversion phase, see [Model Optimizer model conversion](../MO_DG/prepare_model/convert_model/Converting_Model.md)
+ - Improve readability of a model's input and output
+
+## Layout syntax
+
+### Short
+The easiest way is to fully specify each dimension with one alphabetical letter
+
+@sphinxdirective
+
+.. tab:: C++
+
+      .. doxygensnippet:: docs/snippets/ov_layout.cpp
+         :language: cpp
+         :fragment: [ov:layout:simple]
+
+.. tab:: Python
+
+      .. doxygensnippet:: docs/snippets/ov_layout.py
+         :language: python
+         :fragment: [ov:layout:simple]
+
+@endsphinxdirective
+
+This assigns 'N' to first dimension, 'C' to second, 'H' to 3rd and 'W' to 4th
+
+### Advanced
+Advanced syntax allows assigning a word to a dimension. To do this, wrap layout with square brackets `[]` and specify each name separated by comma `,`
+
+@sphinxdirective
+
+.. tab:: C++
+
+      .. doxygensnippet:: docs/snippets/ov_layout.cpp
+         :language: cpp
+         :fragment: [ov:layout:complex]
+
+.. tab:: Python
+
+      .. doxygensnippet:: docs/snippets/ov_layout.py
+         :language: python
+         :fragment: [ov:layout:complex]
+
+@endsphinxdirective
+
+
+### Partially defined layout
+If some dimension is not important, it's name can be set to `?`
+
+@sphinxdirective
+
+.. tab:: C++
+
+      .. doxygensnippet:: docs/snippets/ov_layout.cpp
+         :language: cpp
+         :fragment: [ov:layout:partially_defined]
+
+.. tab:: Python
+
+      .. doxygensnippet:: docs/snippets/ov_layout.py
+         :language: python
+         :fragment: [ov:layout:partially_defined]
+
+@endsphinxdirective
+
+
+### Dynamic layout
+If number of dimensions is not important, ellipsis `...` can be used to specify variadic number of dimensions.
+
+@sphinxdirective
+
+.. tab:: C++
+
+      .. doxygensnippet:: docs/snippets/ov_layout.cpp
+         :language: cpp
+         :fragment: [ov:layout:dynamic]
+
+.. tab:: Python
+
+      .. doxygensnippet:: docs/snippets/ov_layout.py
+         :language: python
+         :fragment: [ov:layout:dynamic]
+
+@endsphinxdirective
+
+### Predefined names
+
+Layout has pre-defined some widely used in computer vision dimension names:
+- N/Batch - batch size
+- C/Channels - channels dimension
+- D/Depth - depth
+- H/Height - height
+- W/Width - width
+
+These names are used in [PreProcessing API](./preprocessing_overview.md) and there is a set of helper functions to get appropriate dimension index from layout
+
+@sphinxdirective
+
+.. tab:: C++
+
+      .. doxygensnippet:: docs/snippets/ov_layout.cpp
+         :language: cpp
+         :fragment: [ov:layout:predefined]
+
+.. tab:: Python
+
+      .. doxygensnippet:: docs/snippets/ov_layout.py
+         :language: python
+         :fragment: [ov:layout:predefined]
+
+@endsphinxdirective
+
+
+### Equality
+
+Layout names are case-insensitive, which means that ```Layout("NCHW") == Layout("nChW") == Layout("[N,c,H,w]")```
+
+### Dump layout
+
+Layout can be converted to string in advanced syntax format. Can be useful for debugging and serialization purposes
+
+@sphinxdirective
+
+.. tab:: C++
+
+      .. doxygensnippet:: docs/snippets/ov_layout.cpp
+         :language: cpp
+         :fragment: [ov:layout:dump]
+
+.. tab:: Python
+
+      .. doxygensnippet:: docs/snippets/ov_layout.py
+         :language: python
+         :fragment: [ov:layout:dump]
+
+@endsphinxdirective
+
+## See also
+
+* <code>ov::Layout</code> C++ class documentation