add force_turbo notes

README.md

@@ -35,6 +35,12 @@ $ ./build_codec2.sh
 $ ./build_rpitx.sh
 $ cd tx && make
 ```
+At the end of `/boot/config.txt` you need:
+```
+gpu_freq=250
+force_turbo=1
+```
+Then reboot your Pi.
 
 ## RTLSDR FSK Receiver
 

build_rpitx.sh

@@ -1,5 +1,9 @@
-# automate building of RpiTx library and applications
+# automate building of RpiTx library
 git clone https://github.com/F5OEO/librpitx
 cd librpitx/src
 make
 cd ../../
+echo "To the end of /boot/config.txt add"
+echo "  gpu_freq=250"
+echo "  force_turbo=1"
+echo "and reboot your Pi"