Update 'README.md' with info on MINGW_ROOT env var for using xc in MSYS2 environment

README.md

@@ -211,6 +211,12 @@ If no leading / is specified in src-or-dest-path, it is assumed to be relative t
 remote user. File operations are all performed as the remote user, so account permissions apply
 as expected.
 
+When running under MSYS2, one must set the MINGW_ROOT environment variable to assist in
+determining how to convert Windows paths to UNIX-style paths. This should be the installation path
+of one's MSYS2 environment (eg., _C:/msys2_). Go's stdlib, under the hood, still uses Windows
+style paths (drive letters and all) to locate other executables and _xc_ uses _tar_ as part of the copy
+functionality.
+
 Local (client) to remote (server) copy:
 ```
 $ xc fileA /some/where/fileB /some/where/else/dirC joebloggs@host-or-ip:remoteDir