Align license statement on README.md to current license

Fix typo

README.md

@@ -1,5 +1,8 @@
+# DMRconfig
+
 DMRconfig is a utility for programming digital radios via USB programming cable.
-Supported radios:
+
+## Supported radios:
 
  * TYT MD-380, Retevis RT3, RT8
  * TYT MD-390
@@ -50,6 +53,24 @@ Update database of contacts from CSV file:
 
 Option -t enables tracing of USB protocol.
 
+## Compilation
+Whenever possible use the `dmrconfig` package provided from by Linux distribution
+
+If you want to compile `dmrconfig`, follow these instructions:
+* Install dependencies
+    * On Ubuntu `sudo apt install git build-essential pkg-config libusb-1.0-0-dev libudev-dev`
+    * On Arch Linux `sudo pacman -S git base-devel libusb`
+    * On Mac OS `brew install pkg-config libusb`
+* Clone this repository
+``` 
+git clone https://github.com/sergev/dmrconfig
+```
+* Compile and install
+```
+make
+sudo make install
+```
+
 ## Permissions
 
 On Linux, a permission to access USB device is required.
@@ -72,20 +93,12 @@ To activate it, run:
 
 Then re-attach the USB cable to the radio.
 
-## Sources
+## License
 
-Sources are distributed freely under the terms of Apache 2.0 license.
-You can download sources via GIT:
+Sources are distributed freely under the terms of BSD 3 license. \
+For more information see the [LICENSE file](https://github.com/OpenRTX/dmrconfig/blob/master/LICENSE)
 
-    git clone https://github.com/sergev/dmrconfig
+## Credits
+DMRconfig was created by Serge Vakulenko KK6ABQ.
 
-
-To build on Linux or Mac OS X, run:
-
-    make
-    make install
-
-
-Regards,
-Serge Vakulenko
-KK6ABQ
+It is currently maintained by the OpenRTX developers.

main.c

@@ -37,6 +37,8 @@ const char *copyright;
 extern char *optarg;
 extern int optind;
 
+int trace_flag = 0;
+
 void usage()
 {
     fprintf(stderr, "DMR Config, Version %s, %s\n", version, copyright);

radio.h

@@ -139,9 +139,9 @@ extern unsigned char radio_mem[];
 //
 // File descriptor of serial port with programming cable attached.
 //
-int radio_port;
+extern int radio_port;
 
 //
 // Read/write progress counter.
 //
-int radio_progress;
+extern int radio_progress;

util.h

@@ -35,7 +35,7 @@ extern const char *copyright;
 //
 // Trace data i/o via the serial port.
 //
-int trace_flag;
+extern int trace_flag;
 
 //
 // Print data in hex format.