README.md: fix typo

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
COPYING: the license is LGPLv2.1, not GPLv3

Most source files are licensed under the GNU LGPL 2.1 or later. The only
exceptions are getopt.h and getopt.c, licensed under LGPL (any version).

Keep in the sources the COPYING file for LGPLv2.1, not GPLv3.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Merge pull request #9 from lucaceresoli/luca/fixes

A couple small fixes