add goroutine example

# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
#
# Author:    Junichi TANAKA <junsan45@gmail.com>
#
# On branch master
#
# Initial commit
#
# Changes to be committed:
#   (use "git rm --cached <file>..." to unstage)
#
#	new file:   .idea/.name
#	new file:   .idea/compiler.xml
#	new file:   .idea/encodings.xml
#	new file:   .idea/misc.xml
#	new file:   .idea/modules.xml
#	new file:   .idea/scopes/scope_settings.xml
#	new file:   .idea/vcs.xml
#	new file:   go-study.iml
#	new file:   src/Animal.go
#	new file:   src/go-study.go
#
# Untracked files:
#   (use "git add <file>..." to include in what will be committed)
#
#	.idea/workspace.xml