minor, map fcntl's O_CREAT and O_RDWR manually to tcbdb's BDBOCREAT and BDBOWRITER

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>
Merge branch 'cmd/add' into next

* cmd/add:
  minor, map fcntl's O_CREAT and O_RDWR manually to tcbdb's BDBOCREAT and BDBOWRITER
doc, provide some examples in README.md

Signed-off-by: Sebastian Freundt <freundt@ga-group.nl>