[docs][python] add conda-forge install instructions (#3544)

* DOC: add conda-forge install instructions

* DOC: add conda-forge instructions

* DOC: fix hyperlink

* DOC: point to installation guide

* add detailed

* Update python-package/README.rst
Co-authored-by: James Lamb <jaylamb20@gmail.com>

* Update python-package/README.rst
Co-authored-by: James Lamb <jaylamb20@gmail.com>

* rm characters

* add pip install

* add :

* Update python-package/README.rst
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* Update python-package/README.rst
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

* remove pip from header

* channel
Co-authored-by: James Lamb <jaylamb20@gmail.com>
Co-authored-by: Nikita Titov <nekit94-08@mail.ru>

docs/Python-Intro.rst

@@ -14,7 +14,7 @@ This document gives a basic walkthrough of LightGBM Python-package.
 Install
 -------
 
-You can install LightGBM via pip
+The preferred way to install LightGBM is via pip:
 
 ::
 

python-package/README.rst

@@ -13,13 +13,12 @@ Preparation
 
 `setuptools <https://pypi.org/project/setuptools>`_ is needed.
 
-Install from `PyPI <https://pypi.org/project/lightgbm>`_ Using ``pip``
-''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
+Install from `PyPI <https://pypi.org/project/lightgbm>`_
+''''''''''''''''''''''''''''''''''''''''''''''''''''''''
 
 .. code:: sh
 
     pip install lightgbm
- 
 
 You may need to install `wheel <https://pythonwheels.com>`_ via ``pip install wheel`` first.
 
@@ -37,7 +36,6 @@ For **macOS** (we provide wheels for 3 newest macOS versions) users:
 
 - For version smaller than 2.1.2, **gcc-7** with **OpenMP** is required.
 
-
 Build from Sources
 ******************
 
@@ -144,6 +142,17 @@ By default, installation in environment with 32-bit Python is prohibited. Howeve
 
 It is **strongly not recommended** to use this version of LightGBM!
 
+Install from `conda-forge channel <https://anaconda.org/conda-forge/lightgbm>`_
+'''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''
+
+If you use ``conda`` to manage Python dependencies, you can install LightGBM using ``conda install``.
+
+**Note**: The `lightgbm conda-forge feedstock <https://github.com/conda-forge/lightgbm-feedstock>`_ is not maintained by LightGBM maintainers.
+
+.. code:: sh
+
+    conda install -c conda-forge lightgbm
+
 Install from GitHub
 '''''''''''''''''''