doc/2.components.md: Add a note about BPN
doc/2.components.md: Add a note about BPN

In meta-debian, BPN presents for the real source package name on Debian
so in some cases, BPN of meta-debian and poky are not same.

Signed-off-by: Trung Do <64081e6b7eb2b24289b8a4e51cef9836ddf28af2@toshiba-tsdv.com>

meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian,meta-debian/meta-debian