README: update to include information about bbappend inclusion
README: update to include information about bbappend inclusion

Update README file to include information about bbappend file inclusion,
telling the users that 'virtualization' needs to be in DISTRO_FEATURES
to make some bbappend files to be effective.

Signed-off-by: Chen Qi <633505cc1c1ae5749a9636f0ba75c172681d2e11@windriver.com>
Signed-off-by: Bruce Ashfield <284cc737d174a260eec2a2a6324a304f84b1ae0f@windriver.com>

lgirdk/meta-virtualization,lgirdk/meta-virtualization,lgirdk/meta-virtualization,lgirdk/meta-virtualization,lgirdk/meta-virtualization