fix wget command, make git-cal executable

The example wget command was using `-o` which is not writing the downloaded file but all log output there. `-O` (uppercase) is the output file switch.

Also added a `chmod` command to make the file executable, which is required to run it.

From the man file:

    ‘-o logfile’
    ‘--output-file=logfile’
    Log all messages to logfile. The messages are normally reported to standard error.
Merge pull request #3 from lennartkoopmann/patch-1

fix wget command, make git-cal executable