Merge pull request #491 from qiaojunfeng/fix/docs_index

Update docs index page

docs/docs/index.md

@@ -1,9 +1,20 @@
-# Welcome to Wannier90 documentation
+# Welcome to the Wannier90 documentation
 
 ![Wannier90 logo](assets/wannier-logo.svg){ width=400 }
 
-This is the home of the documenation of [Wannier90](https://wannier.org),
-which a computer program for maximally-localised Wannier functions (MLWFs).
+This is the home of the documentation of [Wannier90](https://wannier.org),
+which is an open-source code for generating maximally localized Wannier
+functions and using them to compute advanced electronic properties of materials
+with high efficiency and accuracy.
+
+Many electronic structure codes have an interface to Wannier90, and there are
+several post-processing codes that use the output of Wannier90 for further
+analysis and calculation.
+
+For an overview of the main features of Wannier90, please visit the
+[Wannier90 homepage](https://wannier.org/features/).
+
+This documentation contains the following sections:
 
 - [User guide](user_guide/introduction.md)
 - [Tutorials](tutorials/preliminaries.md)