libvirt: document UNDEFINE_KEEP_NVRAM in UndefineFlags docs

src/libvirt-domain.c

@@ -6287,9 +6287,9 @@ virDomainUndefine(virDomainPtr domain)
  * whether this flag is present.  On hypervisors where snapshots do
  * not use libvirt metadata, this flag has no effect.
  *
- * If the domain has any nvram specified, then including
- * VIR_DOMAIN_UNDEFINE_NVRAM will also remove that file, and omitting the flag
- * will cause the undefine process to fail.
+ * If the domain has any nvram specified, the undefine process will fail
+ * unless VIR_DOMAIN_UNDEFINE_KEEP_NVRAM is specified, or if
+ * VIR_DOMAIN_UNDEFINE_NVRAM is specified to remove the nvram file.
  *
  * Returns 0 in case of success, -1 in case of error
  */