Clarify Windows gcc setup instructions.

Author: vadimcn

README.md

@@ -68,7 +68,7 @@ Read ["Installing Rust"] from [The Book].
    # Update package mirrors (may be needed if you have a fresh install of MSYS2)
    $ pacman -Sy pacman-mirrors
 
-   # Choose one based on platform:
+   # Choose one based on platform: (+++ see the note below +++)
    $ pacman -S mingw-w64-i686-toolchain
    $ pacman -S mingw-w64-x86_64-toolchain
 
@@ -89,9 +89,12 @@ Read ["Installing Rust"] from [The Book].
    ```
 > ***Note:*** gcc versions >= 5 currently have issues building LLVM on Windows
 > resulting in a segmentation fault when building Rust. In order to avoid this
-> it may be necessary to obtain an earlier version of gcc such as 4.9.x.
-> Installers for earlier Windows builds of gcc are available at the
-> [Mingw-Builds] project. For more information on this see issue #28260.
+> it may be necessary to obtain an earlier version of gcc such as 4.9.x.  
+> Msys's `pacman` will install the latest version, so for the time being it is
+> recommended to skip gcc toolchain installation step above and use [Mingw-Builds]
+> project's installer instead.  Be sure to add gcc `bin` directory to the path
+> before running `configure`.  
+> For more information on this see issue #28260.
 
 [Mingw-Builds]: http://sourceforge.net/projects/mingw-w64/