Added README and modules folder

Author: Kirill Kornyakov

.gitattributes

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+*.c text
+*.cpp text
+*.h text
+*.hpp text
+*.txt text
+*.mk text
+*.java text

README.md

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-opencv_contrib
-==============
+## Repository for OpenCV's extra modules
 
-Repository for OpenCV's extra modules
+This repository is intended for development of so-called "extra" modules,
+contributed functionality. New modules quite often do not have stable API,
+and they are not well-tested. Thus, they shouldn't be released as a part of
+official OpenCV distribution, since the library maintains binary compatibility,
+and tries to provide decent performance and stability.
+
+So, all the new modules should be developed separately, and published in the
+`opencv_contrib` repository at first. Later, when the module matures and gains
+popularity, it is moved to the central OpenCV repository, and the development team
+provides production quality support for this module.
+
+### How to build OpenCV with extra modules
+
+You can build OpenCV, so it will include the modules from this repository.
+Here is the CMake command for you:
+
+```
+$ cd <opencv_build_directory>
+$ cmake -DOPENCV_EXTRA_MODULES_PATH=<opencv_contrib> <opencv_source_directory>
+$ make -j5
+```
+
+As the result, OpenCV will be built in the `<opencv_build_directory>` with all
+modules from `opencv_contrib` repository. If you don't want all of the modules,
+use CMake's `BUILD_opencv_*` options. Like in this example:
+
+```
+$ cmake -DOPENCV_EXTRA_MODULES_PATH=<opencv_contrib> -DBUILD_opencv_legacy=OFF <opencv_source_directory>
+```

modules/README.md

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+Please put your module here.