tests/test-stbt-run.py: added missing hyphen in test_get_config()

Due to a missing hyphen, the test_get_config() was calling `stbt run`
(which launched /usr/libexec/stbt) instead of the `stbt-run` in the
top-level source directory.
README: Link to DirectFBSource GStreamer element
README: Minor correction: We only support one *lirc*-based ir blaster per PC
stbt-run: Add missing newline to log message