[docs] Simplify the python installation instruction (#3378)

* Update Python-Intro.rst

* Update README.rst

docs/Python-Intro.rst

@@ -14,14 +14,13 @@ This document gives a basic walkthrough of LightGBM Python-package.
 Install
 -------
 
-Install Python-package dependencies,
-``setuptools``, ``wheel``, ``numpy`` and ``scipy`` are required, ``scikit-learn`` is required for sklearn interface and recommended:
+You can install LightGBM via pip
 
 ::
 
-    pip install setuptools wheel numpy scipy scikit-learn -U
+    pip install lightgbm
 
-Refer to `Python-package`_ folder for the installation guide.
+Refer to `Python-package`_ folder for the detailed installation guide.
 
 To verify your installation, try to ``import lightgbm`` in Python:
 

python-package/README.rst

@@ -16,6 +16,13 @@ Preparation
 Install from `PyPI <https://pypi.org/project/lightgbm>`_ Using ``pip``
 ''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 
+.. code:: sh
+
+    pip install lightgbm
+ 
+
+You may need to install `wheel <https://pythonwheels.com>`_ via ``pip install wheel`` first.
+
 For **Windows** users, `VC runtime <https://support.microsoft.com/en-us/help/2977003/the-latest-supported-visual-c-downloads>`_ is needed if **Visual Studio** (2015 or newer) is not installed.
 
 For **Linux** users, **glibc** >= 2.14 is required.
@@ -28,11 +35,6 @@ For **macOS** (we provide wheels for 3 newest macOS versions) users:
 
 - For version smaller than 2.1.2, **gcc-7** with **OpenMP** is required.
 
-Install `wheel <https://pythonwheels.com>`_ via ``pip install wheel`` first. After that download the wheel file and install from it:
-
-.. code:: sh
-
-    pip install lightgbm
 
 Build from Sources
 ******************