Update `README.md` to address old `bison` problem on macOS.
MODIFY
README.md
README.md
@@ -46,6 +46,10 @@ To run the tests, execute the following from the project's root directory.
$ rake test
+Note: `bison` bundled with MacOS is too old to compile `mruby`.
+Try `brew install bison` and follow the instuction shown to update
+the `$PATH` to compile `mruby`.
+
## Building documentation
There are two sets of documentation in mruby: the mruby API (generated by yard) and C API (Doxygen)

Update `README.md` to address old `bison` problem on macOS.