docs: restructure and expand documentation

Documentation restructure:
- Reorganized into topic-based sections: getting-started/, guide/,
  examples/, api/, migration/
- Added installation guide with Qt SVG dependency note
- Added quickstart tutorial with step-by-step screenshots
- Expanded data-flow guide with validation and processing status
- Added FAQ and v2-to-v3 migration guide

Screenshots and diagrams:
- Added 19 screenshots in docs/_static/screenshots/
- Added PlantUML architecture diagrams in docs/_static/diagrams/
- Moved README showcase images to assets/
- Increased image sizes for better visibility

Build configuration:
- Fixed Sphinx SOURCEDIR path
- Added venv to exclude_patterns

Author: paceholder

README.rst

@@ -34,7 +34,7 @@ Warning
 Branches
 --------
 
-There are branchses ``v2`` and ``v3`` for versions ``2.x.x`` and ``3.x``
+There are branches ``v2`` and ``v3`` for versions ``2.x.x`` and ``3.x``
 respectively. The branch ``master`` contains the latest dev state.
 
 
@@ -74,7 +74,7 @@ Dependencies
 ------------
 
 * Qt >5.15
-* CMake 3.8
+* CMake 3.11
 * Catch2
 
 
@@ -118,7 +118,7 @@ For building a static lib use:
 
 ::
 
-    cmake .. -BUILD_SHARED_LIBS=off
+    cmake .. -DBUILD_SHARED_LIBS=off
 
 Linux
 -----
@@ -193,9 +193,9 @@ For detailed testing documentation, see the `Testing Guide <https://qtnodes.read
 Help Needed
 ===========
 
-#. Python wrappring using PySide.
+#. Python wrapping using PySide.
 #. QML frontend.
-#. Wirting a ClangFormat config.
+#. Writing a ClangFormat config.
 
 Any suggestions are welcome!
 
@@ -220,7 +220,7 @@ Contribution
    #. Describe your issue in details
    #. Provide some use cases.
 
-#. I maintain this probject in my free time, when I am not busy with my work or
+#. I maintain this project in my free time, when I am not busy with my work or
    my family. **If I do not react or do not answer for too long, please ping
    me**.
 
@@ -288,7 +288,7 @@ every automotive developer. Thanks to modularity it is easy to implement new,
 custom features.
 
 
-.. image:: docs/_static/showcase_CANdevStudio.png
+.. image:: assets/showcase-candevstudio.png
 
 
 Chigraph
@@ -297,7 +297,7 @@ Chigraph
 `Chigraph <https://github.com/chigraph/chigraph>`_ is a visual programming
 language for beginners that is unique in that it is an intuitive flow graph:
 
-.. image:: docs/_static/chigraph.png
+.. image:: assets/chigraph.png
 
 
 It features easy bindings to C/C++, package management, and a cool interface.
@@ -310,4 +310,4 @@ Spkgen particle editor
 particles engine that uses a node-based interface to create particles effects for
 games
 
-.. image:: docs/_static/spkgen.png
+.. image:: assets/spkgen.png

docs/_static/chigraph.png assets/chigraph.pngdocs/_static/chigraph.png renamed to assets/chigraph.png

@@ -5,7 +5,7 @@
 # from the environment for the first two.
 SPHINXOPTS    ?=
 SPHINXBUILD   ?= sphinx-build
-SOURCEDIR     = source
+SOURCEDIR     = .
 BUILDDIR      = build
 
 # Put it first so that "make" without argument is like "make help".

docs/_static/showcase_CANdevStudio.png assets/showcase-candevstudio.pngdocs/_static/showcase_CANdevStudio.png renamed to assets/showcase-candevstudio.png

@@ -0,0 +1,53 @@
+@startuml architecture-diagram
+!theme plain
+skinparam backgroundColor #2B2B2B
+skinparam defaultFontColor #E0E0E0
+skinparam classBorderColor #606060
+skinparam classBackgroundColor #3C3F41
+skinparam arrowColor #A0A0A0
+skinparam noteBorderColor #606060
+skinparam noteBackgroundColor #4A4D4F
+
+skinparam rectangle {
+    BackgroundColor #3C3F41
+    BorderColor #606060
+    FontColor #E0E0E0
+}
+
+rectangle "Your Application" as app #4A5568 {
+    rectangle "Your Data\n(nodes, connections,\npositions, values)" as data #718096
+}
+
+rectangle "QtNodes Library" as lib #2D3748 {
+    rectangle "AbstractGraphModel\n(or DataFlowGraphModel)" as model #4A5568
+    rectangle "BasicGraphicsScene\n(or DataFlowGraphicsScene)" as scene #4A5568
+    rectangle "GraphicsView" as view #4A5568
+}
+
+rectangle "User Interface" as ui #1A202C {
+    rectangle "Window with\ninteractive nodes" as window #2D3748
+}
+
+data -right-> model : "implements"
+model -right-> scene : "visualizes"
+scene -right-> view : "displays in"
+view -right-> window : "renders to"
+
+note bottom of model
+  You subclass this
+  to store your graph data
+end note
+
+note bottom of scene
+  Automatically creates
+  graphics objects from
+  model data
+end note
+
+note bottom of view
+  Handles zoom, pan,
+  selection, and
+  user interactions
+end note
+
+@enduml

docs/_static/spkgen.png assets/spkgen.pngdocs/_static/spkgen.png renamed to assets/spkgen.png

@@ -0,0 +1,48 @@
+@startuml dataflow-diagram
+!theme plain
+skinparam backgroundColor #2B2B2B
+skinparam defaultFontColor #E0E0E0
+skinparam componentBorderColor #606060
+skinparam componentBackgroundColor #3C3F41
+skinparam arrowColor #4299E1
+skinparam noteBorderColor #606060
+skinparam noteBackgroundColor #4A4D4F
+
+skinparam rectangle {
+    BackgroundColor #3C3F41
+    BorderColor #606060
+    FontColor #E0E0E0
+    RoundCorner 15
+}
+
+rectangle "Source Node\n(NumberSourceDataModel)" as source #48BB78 {
+}
+
+rectangle "Operator Node\n(AdditionModel)" as operator #4299E1 {
+}
+
+rectangle "Display Node\n(NumberDisplayDataModel)" as display #ED8936 {
+}
+
+source -right-> operator : "outData()"
+operator -right-> display : "outData()"
+
+note bottom of source
+  **Emits data**
+  Creates values
+  (e.g., number input)
+end note
+
+note bottom of operator
+  **Processes data**
+  Receives via setInData()
+  Outputs via outData()
+end note
+
+note bottom of display
+  **Consumes data**
+  Receives and shows
+  the final result
+end note
+
+@enduml