rtl_sdr: add page (#7029)

pages/common/rtl_sdr.md

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+# rtl_sdr
+
+> Raw data recorder for RTL-SDR receivers.
+> Data is encoded using I/Q sampling (aka quadrature sampling).
+> More information: <https://osmocom.org/projects/rtl-sdr/wiki/Rtl-sdr>.
+
+- Save RAW data from a frequency (specified in Hz) to a file:
+
+`rtl_sdr -f {{100000000}} {{path/to/file}}`
+
+- Pipe data to another program:
+
+`rtl_sdr -f {{100000000}} - | {{aplay}}`
+
+- Read a specified number of samples:
+
+`rtl_sdr -f {{100000000}} -n {{20}} -`
+
+- Specify the sample rate in Hz (ranges 225001-300000 and 900001-3200000):
+
+`rtl_sdr -f {{100000000}} -s {{2400000}} -`
+
+- Specify the device by its index:
+
+`rtl_sdr -f {{100000000}} -d {{0}} -`
+
+- Specify the gain:
+
+`rtl_sdr -f {{100000000}} -g {{20}} -`
+
+- Specify the output block size:
+
+`rtl_sdr -f {{100000000}} -b {{9999999}} -`
+
+- Use synchronous output:
+
+`rtl_sdr -f {{100000000}} -S -`