Add my fix to building on OS X

In the hope it will be helpful.  I don't see another fix yet.  And I'm
apparently the only person suffering from this (so far)

Author: lizmat

README.pod

@@ -71,6 +71,24 @@ to be executed from the command line.  Each line entered is treated
 as a separate compilation unit, however (which means that subroutines
 are preserved after they are defined, but variables are not).
 
+=head2 Troubleshooting
+
+=head3 OS X
+
+On OS X, it appears that configuration fails in some configurations:
+
+  3rdparty/libuv/include/uv-darwin.h:26:11: fatal error: 'mach/mach.h' file not found
+
+Should this happen to you, then a solution might be the following:
+
+    $ cd MoarVM/3rdparty/libuv/include
+    $ ln -s /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/usr/include/mach
+    $ cd ../../../..
+    $ # run the Configure again
+
+Note that the 10.9 in the above, represents the major version of OS X being
+used.  On Mavericks use 10.9 (like above), on Yosemite use 10.10.
+
 =head2 Differences from nqp-rx
 
 NQP is the successor implementation of "nqp-rx" [2].  Unlike nqp-rx,