[docs] refined title RTD page and renamed js file (#1539)

* added definition of LightGBM to ReadTheDocs main page

* bold LightGBM

* Rename rst_links_fix.js to script.js

* fix js name in config

docs/conf.py

@@ -132,4 +132,4 @@ htmlhelp_basename = 'LightGBMdoc'
 
 
 def setup(app):
-    app.add_javascript("js/rst_links_fix.js")
+    app.add_javascript("js/script.js")

docs/index.rst

@@ -6,6 +6,16 @@
 Welcome to LightGBM's documentation!
 ====================================
 
+**LightGBM** is a gradient boosting framework that uses tree based learning algorithms. It is designed to be distributed and efficient with the following advantages:
+
+- Faster training speed and higher efficiency
+- Lower memory usage
+- Better accuracy
+- Parallel and GPU learning supported
+- Capable of handling large-scale data
+
+For more details, please refer to `Features <./Features.rst>`__.
+
 .. toctree::
    :maxdepth: 1
    :caption: Contents: