Merge pull request #16165 from sajarindider:macOS_install

* doc: added macOS installation guide

* doc: added clarification and corrections

* docs: introduction entry, lowercase file names and ids

doc/tutorials/introduction/macos_install/macos_install.markdown

+Installation in MacOS {#tutorial_macos_install}
+=====================
+
+The following steps have been tested for MacOSX (Mavericks) but should work with other versions as well.
+
+Required Packages
+-----------------
+
+-   CMake 3.9 or higher
+-   Git
+-   Python 2.7 or later and Numpy 1.5 or later
+
+This tutorial will assume you have [Python](https://docs.python.org/3/using/mac.html),
+[Numpy](https://docs.scipy.org/doc/numpy-1.10.1/user/install.html) and
+[Git](https://www.atlassian.com/git/tutorials/install-git) installed on your machine.
+
+@note
+OSX comes with Python 2.7 by default, you will need to install Python 3.8 if you want to use it specifically.
+
+@note
+If you XCode and XCode Command Line-Tools installed, you already have git installed on your machine.
+
+Installing CMake
+----------------
+-# Find the version for your system and download CMake from their release's [page](https://cmake.org/download/)
+
+-# Install the dmg package and launch it from Applications. That will give you the UI app of CMake
+
+-# From the CMake app window, choose menu Tools --> Install For Command Line Use.
+
+-# Install folder will be /usr/bin/ by default, submit it by choosing Install command line links.
+
+-# Test that it works by running
+    @code{.bash}
+    cmake --version
+    @endcode
+
+Getting OpenCV Source Code
+--------------------------
+
+You can use the latest stable OpenCV version or you can grab the latest snapshot from our
+[Git repository](https://github.com/opencv/opencv.git).
+
+### Getting the Latest Stable OpenCV Version
+
+-   Go to our [downloads page](http://opencv.org/releases.html).
+-   Download the source archive and unpack it.
+
+### Getting the Cutting-edge OpenCV from the Git Repository
+
+Launch Git client and clone [OpenCV repository](http://github.com/opencv/opencv).
+If you need modules from [OpenCV contrib repository](http://github.com/opencv/opencv_contrib) then clone it as well.
+
+For example
+@code{.bash}
+cd ~/<my_working_directory>
+git clone https://github.com/opencv/opencv.git
+git clone https://github.com/opencv/opencv_contrib.git
+@endcode
+Building OpenCV from Source Using CMake
+---------------------------------------
+
+-#  Create a temporary directory, which we denote as `<cmake_build_dir>`, where you want to put
+    the generated Makefiles, project files as well the object files and output binaries and enter
+    there.
+
+    For example
+    @code{.bash}
+    mkdir build_opencv
+    cd build_opencv
+    @endcode
+
+    @note It is good practice to keep clean your source code directories. Create build directory outside of source tree.
+
+-#  Configuring. Run `cmake [<some optional parameters>] <path to the OpenCV source directory>`
+
+    For example
+    @code{.bash}
+    cmake -DCMAKE_BUILD_TYPE=Release -DBUILD_EXAMPLES=ON ../opencv
+    @endcode
+
+    or cmake-gui
+
+    -   set full path to OpenCV source code, e.g. `/home/user/opencv`
+    -   set full path to `<cmake_build_dir>`, e.g. `/home/user/build_opencv`
+    -   set optional parameters
+    -   run: "Configure"
+    -   run: "Generate"
+
+-#  Description of some parameters
+    -   build type: `CMAKE_BUILD_TYPE=Release` (or `Debug`)
+    -   to build with modules from opencv_contrib set `OPENCV_EXTRA_MODULES_PATH` to `<path to
+        opencv_contrib>/modules`
+    -   set `BUILD_DOCS=ON` for building documents (doxygen is required)
+    -   set `BUILD_EXAMPLES=ON` to build all examples
+
+-#  [optional] Building python. Set the following python parameters:
+    -   `PYTHON3_EXECUTABLE = <path to python>`
+    -   `PYTHON3_INCLUDE_DIR = /usr/include/python<version>`
+    -   `PYTHON3_NUMPY_INCLUDE_DIRS =
+        /usr/lib/python<version>/dist-packages/numpy/core/include/`
+    @note
+    To specify Python2 versions, you can replace `PYTHON3_` with `PYTHON2_` in the above parameters.
+
+-#  Build. From build directory execute *make*, it is recommended to do this in several threads
+
+    For example
+    @code{.bash}
+    make -j7 # runs 7 jobs in parallel
+    @endcode
+
+-#  To use OpenCV in your CMake-based projects through `find_package(OpenCV)` specify `OpenCV_DIR=<path_to_build_or_install_directory>` variable.
+
+@note
+You can also use a package manager like [Homebrew](https://brew.sh/)
+or [pip](https://pip.pypa.io/en/stable/) to install releases of OpenCV only (Not the cutting edge).

doc/tutorials/introduction/table_of_content_introduction.markdown

@@ -110,6 +110,14 @@ Additionally you can find very basic sample source code to introduce you to the
 
     Modify Android camera preview with OpenCL
 
+-   @subpage tutorial_macos_install
+
+    _Compatibility:_ \> OpenCV 3.4.x
+
+    _Author:_ [\@sajarindider](https://github.com/sajarindider)
+
+    We will learn how to setup OpenCV in MacOS.
+
 -   @subpage tutorial_ios_install
 
     _Compatibility:_ \> OpenCV 2.4.2