[Doc] Add instructions for Windows users to install VC2015 redistributable (#3071)

* add instructions for VC2015 redist install

* fix typo

README.md

@@ -350,7 +350,7 @@ DGL should work on
 
 * all Linux distributions no earlier than Ubuntu 16.04
 * macOS X
-* Windows 10
+* Windows 10 (with [VC2015 Redistributable](https://www.microsoft.com/en-us/download/details.aspx?id=48145) Installed)
 
 DGL requires Python 3.6 or later.
 

docs/source/faq.rst

 Frequently Asked Questions (FAQ)
 ================================
 
-For frequently asked questios, refer to `this post <https://discuss.dgl.ai/t/frequently-asked-questions-faq/1681>`__.
+For frequently asked questions, refer to `this post <https://discuss.dgl.ai/t/frequently-asked-questions-faq/1681>`__.

docs/source/install/index.rst

@@ -23,6 +23,10 @@ Install from Conda or Pip
 We recommend installing DGL by ``conda`` or ``pip``.
 Check out the instructions on the `Get Started page <https://www.dgl.ai/pages/start.html>`_.
 
+.. note::
+
+   For Windows users: you will need to install `Visual C++ 2015 Redistributable <https://www.microsoft.com/en-us/download/details.aspx?id=48145>`_.
+
 .. _install-from-source:
 
 Install from source