[doc] more docs for python package (#1726)

* Update README.rst

* Update README.rst

* separate list item for <2.1.2 version and future -> present time

python-package/README.rst

@@ -18,11 +18,15 @@ Install from `PyPI <https://pypi.org/project/lightgbm>`_ Using ``pip``
 
 For **Windows** users, `VC runtime <https://go.microsoft.com/fwlink/?LinkId=746572>`_ is needed if **Visual Studio** (2015 or 2017) is not installed.
 
-For **macOS** users, **gcc** with **OpenMP** support must be installed first. Refer to `Installation Guide <https://github.com/Microsoft/LightGBM/blob/master/docs/Installation-Guide.rst#gcc>`__ for installation of **gcc** with **OpenMP** support.
+For **Linux** users, **glibc** >= 2.14 is required.
 
-For **macOS** users, latest versions of LightGBM are built with **gcc-8** and cannot be launched on systems with **gcc-7** and earlier. You should update your **gcc** compiler if you don't want to build from sources or install LightGBM 2.1.1 which is the last version built with **gcc-7**.
+For **macOS** users:
 
-For **macOS** users, starting from version 2.2.1, the library file in distribution wheels will be built by the **Apple Clang** compiler. This means that you won't need to install the **gcc** compiler anymore. Instead of that you'll need to install the **OpenMP** library, which is required for running LightGBM on the system with the **Apple Clang** compiler. You can install the **OpenMP** library by the following command: ``brew install libomp``.
+- Starting from version 2.2.1, the library file in distribution wheels is built by the **Apple Clang** (Xcode_9.4.1) compiler. This means that you don't need to install the **gcc** compiler anymore. Instead of that you need to install the **OpenMP** library, which is required for running LightGBM on the system with the **Apple Clang** compiler. You can install the **OpenMP** library by the following command: ``brew install libomp``.
+
+- For version smaller than 2.2.1 and not smaller than 2.1.2, **gcc-8** with **OpenMP** support must be installed first. Refer to `Installation Guide <https://github.com/Microsoft/LightGBM/blob/master/docs/Installation-Guide.rst#gcc>`__ for installation of **gcc-8** with **OpenMP** support.
+
+- For version smaller than 2.1.2, **gcc-7** with **OpenMP** is required.
 
 Install `wheel <http://pythonwheels.com>`_ via ``pip install wheel`` first. After that download the wheel file and install from it: