Update installation instructions for Windows

doc/source/installation.rst

@@ -3,7 +3,9 @@ Installing Ray
 
 .. tip:: Join our `community slack <https://forms.gle/9TSdDYUgxYs8SA9e8>`_ to discuss Ray!
 
-Ray currently supports MacOS and Linux. Windows support is planned for the future.
+Ray currently supports MacOS and Linux.
+Windows support is under development and still experimental/unstable.
+Bugs, process/resource leaks, or other incompatibilities may still exist.
 
 Latest stable version
 ---------------------
@@ -14,14 +16,16 @@ You can install the latest stable version of Ray as follows.
 
   pip install -U ray  # also recommended: ray[debug]
 
+Windows users: Please also ensure the Visual C++ runtime is installed (see "Dependencies" below).
 
 .. _install-nightlies:
 
 Latest Snapshots (Nightlies)
 ----------------------------
 
 Here are links to the latest wheels (which are built for each commit on the
-master branch). To install these wheels, run the following command:
+master branch). To install these wheels, use the following ``pip`` command and wheels
+instead of the ones above:
 
 .. code-block:: bash
 
@@ -98,12 +102,25 @@ For MacOS, run the following commands:
 
   pip install cython==0.29.0 pytest
 
+For Windows, ensure the latest `Visual C++ runtime` is installed before using Ray.
+Otherwise, you may receive an error similar to the following when Ray fails to find
+the runtime library files (e.g. ``VCRUNTIME140_1.dll``):
+
+.. code-block:: bash
+
+  FileNotFoundError: Could not find module '_raylet.pyd' (or one of its dependencies).
+
+.. _`Visual C++ Runtime`: https://aka.ms/vs/16/release/vc_redist.x64.exe
+
 
 Install Ray
 ~~~~~~~~~~~
 
 Ray can be built from the repository as follows.
 
+We recommend avoiding paths with spaces or other special characters to avoid potential problems.
+However, should you encounter any related issues, please let us know.
+
 .. code-block:: bash
 
   git clone https://github.com/ray-project/ray.git
@@ -129,6 +146,8 @@ If you would like to use the dashboard, you will additionally need to install
 `Node.js`_ and build the dashboard before installing Ray. The relevant build
 steps are included in the installation instructions above.
 
+(Note that the dashboard may not yet work on Windows.)
+
 .. _`Node.js`: https://nodejs.org/
 
 The dashboard requires a few additional Python packages, which can be installed