Update README.md

Author: JohandeGraaf

README.md

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 # gr-fsk4
-Custom GNU Radio \(Companion\) blocks for decoding 4L-FSK, APCO-25 and RDLAP.
+Custom GNU Radio \(Companion\) blocks for demodulating 4L-FSK (4 Level Frequency-Shift Keying) signals, and APCO-25 and RDLAP protocol processing.
 
 This module is the updated version of [gr-fsk4](http://www.qsl.net/kb9mwr/projects/dv/apco25/GnuradioFourLevelFSK.pdf)
 \([code](http://www.qsl.net/kb9mwr/projects/dv/apco25/gr-fsk4-22Apr08.tar.gz)\) for GNU Radio 3.7+. The code in this repository borrows heavily from various GNU Radio examples and components which fall under the GNU General Public License. All additional modifications and code also fall under GNU General Public License.