Dependencies.md

+This addon depends on several libraries, and you have to install at least some
+of them in order to use Sverchok-Extra. If you do not need all features, you
+may install only one or two of libraries, but you have to install at least
+something, otherwise Sverchok-Extra will just do nothing.
+
+One thing you will have to install anyway if you want to use Sverchok-Extra is
+[pip][6]. All libraries are installed with it.
+
+### Simple dependencies installation UI
+
+Some of dependencies can be installed easily, by just running `pip`. For such
+dependencies, Sverchok-Extra supports easy-to-use installation user interface.
+To use it, navigate to Edit => Preferences, then locate Sverchok-Extra
+preferences under Addons section:
+
+![Settings](https://user-images.githubusercontent.com/284644/74547121-74555380-4f6d-11ea-8388-80421a04fc3f.png)
+
+The dialog shows current status of all dependencies. For dependencies that can
+be installed by `pip`, but are not yet installed, this dialog will show an
+"Install" button. You'll have just to press the button and wait for when
+Blender will say that the library is installed. If there will be any errors
+during installation, Blender will report it and print details into console
+output.
+
+For dependencies that can not be installed that easily, the dialog contains a
+button which opens the browser on an official web site of corresponding
+library, so you can find installation instructions.
+
+The following sections of this document will be useful if you can not install
+the library by pressing the button. For libraries that can not be that easily
+installed by `pip`, this document contains only short instructions. Please
+refer to web sites of corresponding libraries for complete instructions and
+support.
+
+All commands provided in this document are for Linux-based systems. For Windows
+and MacOS, commands may differ a bit, but the general idea will be the same.
+
+### Install pip
+
+In some cases, it may appear that Blender's python already knows about your
+system's installation of python (python is usually installed by default on most
+Linux distros). In such cases, you may use just `pip install something` to
+install libraries.
+
+There are two known ways to install `pip` into Blender.
+
+#### Option 1
+
+This I tested on latest Blender 2.81 builds. The similar instructions should
+work for other Blender 2.8x versions.
+
+    $ /path/to/blender/2.xx/python/bin/python3 -m ensurepip
+    $ /path/to/blender/2.xx/python/bin/python3 -m pip install --upgrade pip setuptools wheel
+
+(exact name of `python` executable depends on specific blender build).
+
+#### Option 2
+
+If, for some reason, Option 1 does not work for you (on some system Python says
+`no module named ensurepip`), then you have to do the following:
+
+1. Download [get-pip.py][13] script
+2. Run it with Blender's python:
+
+    $ /path/to/blender/2.xx/python/bin/python3.7m /path/to/get-pip.py
+
+Please refer to [official pip site][14] for official installation instructions.
+
+### Install SciPy
+
+    $ /path/to/blender/2.xx/python/bin/python3.7m -m pip install -U scipy
+
+### Install SciKit-Image
+
+    $ /path/to/blender/2.xx/python/bin/python3.7m -m pip install -U scikit-image
+
+### Install Circlify
+
+    $ /path/to/blender/2.xx/python/bin/python3.7m -m pip install -U circlify
+
+### Install PyMCubes
+
+This is more complex. First, you have to install [Cython][7]:
+
+    $ /path/to/blender/2.xx/python/bin/python3 -m pip install Cython
+
+Then you have to set up a build environment for Cython. You will need 1) to
+install development files for Python (such as `Python.h` and others), and 2) to
+explain Blender's python where to find them. **Note**: you have to have headers
+for exactly the same version of Python that your Blender build is using.
+
+On Debian/Ubuntu, you can install Python's development files by `apt-get
+install libpython3.7-dev` for `python3.7m` used in Blender 2.80/2.81. On other
+Linux distros, the command will be similar. On Windows or MacOS this can be
+more tricky, I did not try.
+
+You have to somehow tell Blender's built-in python where to look for headers.
+I've found the simplest way is to do
+
+    $ ln -s /usr/include/python3.7m/* /path/to/blender/2.xx/python/include/python3.7m/
+
+There may be more correct way, but I do not know it.
+
+After that, you can install PyMCubes by
+
+    $ /path/to/blender/2.xx/python/bin/python3.7m -m pip install -U PyMCubes
+
+### Install Geomdl
+
+In the simplest case, you can install Geomdl by
+
+    $ /path/to/blender/2.xx/python/bin/python3.7m -m pip install -U geomdl
+
+but this way you will get pure-python library, which is very slow. If you want
+it fast, then you have to install Cython (see previous paragraph for
+instruction). After you installed Cython, you can install "cythonized" geomdl
+as it is described in [Geomdl instruction][9]:
+
+    $ /path/to/blender/2.xx/python/bin/python3 -m pip install geomdl --install-option="--use-cython"
+