install error without libmagic

/Users/mw82/.rvm/rubies/ruby-2.2.2/bin/ruby -r ./siteconf20150501-29651-ub6bv6.rb extconf.rb
checking for magic_open() in -lmagic... yes
checking for magic.h... yes
checking for file/patchlevel.h... no
creating Makefile

make "DESTDIR=" clean

make "DESTDIR="
compiling filemagic.c
filemagic.c:73:55: warning: use of logical '||' with constant operand [-Wconstant-logical-operand]
      "failed to initialize magic cookie (%d)", errno || -1);
                                                      ^  ~~
filemagic.c:73:55: note: use '|' for a bitwise operation
      "failed to initialize magic cookie (%d)", errno || -1);
                                                      ^~
                                                      |
1 warning generated.
linking shared-object filemagic/ruby_filemagic.bundle

make "DESTDIR=" install
/usr/bin/install -c -m 0755 ruby_filemagic.bundle ./.gem.20150501-29651-1efwg0i/filemagic

osx ruby 2.2.2

when use

brew install libmagic

then it is OK

should we add this in readme?

https://github.com/blackwinter/ruby-filemagic/issues/2

blackwinter / ruby-filemagic

install error without libmagic #15