Add comments on using board file remote-gdbserver-on-localhost.exp

This commit is to add comments on using this board file and the
requirements on localhost.

gdb/testsuite:

2015-06-22  Yao Qi  <yao.qi@linaro.org>

	* boards/remote-gdbserver-on-localhost.exp: Add comments.

gdb/testsuite/ChangeLog

@@ -1,3 +1,7 @@
+2015-06-22  Yao Qi  <yao.qi@linaro.org>
+
+	* boards/remote-gdbserver-on-localhost.exp: Add comments.
+
 2015-06-22  Yao Qi  <yao.qi@linaro.org>
 
 	* lib/gdb.exp (skip_hw_breakpoint_tests): Return 0 for target

gdb/testsuite/boards/remote-gdbserver-on-localhost.exp

@@ -27,6 +27,9 @@ set_board_info compiler  "[find_gcc]"
 
 process_multilib_options ""
 
+# The sshd should be running on localhost and ssh key should be
+# correctly set up that you ssh to localhost without having to type
+# password.
 set_board_info rcp_prog "/usr/bin/scp"
 set_board_info rsh_prog "/usr/bin/ssh"
 set_board_info protocol standard