update docs

Author: arch

docs/app/docs/user-guide/algorithms.md

@@ -22,8 +22,8 @@ Idea: By using [OpenCV Tracker](https://learnopencv.com/object-tracking-using-op
 
 ### Improvements
 
-- You can change the OpenCV tracker in the source code which predicts the position. OpenCV offers several trackers which differ in prediction accuracy and processing speed. See also [OpenCV Tracker](https://learnopencv.com/object-tracking-using-opencv-cpp-python/).
+- You can change the OpenCV tracker which predicts the position. OpenCV offers several trackers which differ in prediction accuracy and processing speed. See also [OpenCV Tracker](https://learnopencv.com/object-tracking-using-opencv-cpp-python/).
 
 - You can set the number of frames that are interpolated by the `skip_frames` parameter. 0 means that the OpenCV tracker delivers a prediction for each frame. This is slower but more accurate. Or if greater than zero, the individual frames are skipped and then the tracking boxes are interpolated, which increases the processing speed but decreases the accuracy. I have set the value to 1, i.e. every 2nd frame is skipped and interpolated. Which provides a good mix of accuracy and speed.
 
-- It is recommended to use a low resolution video e.g. 4K for generating the funscript actions, as the processing speed is higher.
+- It is recommended to use a low resolution video e.g. 1080p or 4K for generating the funscript actions, as the processing speed is higher.

docs/app/docs/user-guide/build.md

@@ -65,3 +65,14 @@ sudo pacman -Sy python-opencv python-pyqt5
 ```
 
 All other required python packages can be installed from pip.
+
+## Flatpak
+
+The repository contains an flatpak build recipe that can be used to build an flatpak app. You can build the flatpak with the `build_flatpak.sh` script in the project root directory. The build script generate the `PythonFunscriptEditor.flatpak` package that can be installed with `flatpak install --user PythonFunscriptEditor.flatpak` on the system.
+
+Limitation of the flatpak application:
+
+- No public release in a flatpak repository available. You have to build the flatpak local.
+- Slow build process.
+- Flatpak need non-privileged user namespaces enabled (`sysctl kernel.unprivileged_userns_clone=1'`).
+- The System-Theme is not applied to the application. The problem is that my recipe use conda packages which isolates the python packages inside the flatpak sandbox and we have no access to the system theme. To fix this we have to build all python packages in the flatpak recipe from source and include the system theme inside the flatpak.