Example for --disable-coverage-init

[dkasak]

If I understood the docs correctly, --disable-coverage-init is supposed to allow updating already existing coverage information with new test cases. However, I was unable to make it work, since it either complains that an existing cov directory was found or, if told to overwrite the directory with -O, it says /tmp/afl-ramdisk/out/cov/lcov/trace.lcov_info_final.

Could you add an example of this flag's usage to the README?