Notify adb missing

There are many user who encounters missing adb.
To stop things happens again, we check it and show
sexy response to user.

Signed-off-by: yuchenlin <npes87184@gmail.com>

app/src/command.h

@@ -32,7 +32,7 @@
 #endif
 # define NO_EXIT_CODE -1
 
-process_t cmd_execute(const char *path, const char *const argv[]);
+int cmd_execute(const char *path, const char *const argv[], process_t *process);
 SDL_bool cmd_terminate(process_t pid);
 SDL_bool cmd_simple_wait(process_t pid, exit_code_t *exit_code);