Made a note on the apt-get installer's package name.
This fixes issue #59.
diff --git a/README.mdown b/README.mdown
index aeb50fb..ecaa11a 100644
--- a/README.mdown
+++ b/README.mdown
@@ -43,7 +43,8 @@
git-flow depends on the availability of the command line utility `getopt`,
which may not be available in your Unix/Linux environment. Please use your
favorite package manager to install `getopt`. For Cygwin, install the
-`util-linux` package to get `getopt`.
+`util-linux` package to get `getopt`. If you use `apt-get` as your install
+manager, the package name is `opt`.
Integration with your shell