Update compiling.md
neither `make release` nor `make debug` would execute properly on a fresh clone of the directory until i ran `make clean`. system is linux mint  - 5.3.0-53-generic #47~18.04.1-Ubuntu SMP Thu May 7 13:10:50 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
@@ -110,8 +110,9 @@ or execute (Debian-based systems only): `apt-get install gcc build-essential cma
### Building
1. Change into the project source directory: `cd stlink`
-2. Run `make release` to create the _Release_ target
-3. Run `make debug` to create the _Debug_ target (_optional_)<br />
+2. Run `make clean` -- required by some linux variants.
+3. Run `make release` to create the _Release_ target
+4. Run `make debug` to create the _Debug_ target (_optional_)<br />
The debug target is only necessary in order to modify the sources and to run under a debugger.
The top level Makefile is just a handy wrapper for:
