rados: add missing doc comment for OpenIOContext function

Signed-off-by: John Mulligan <jmulligan@redhat.com>

rados/conn.go

@@ -82,6 +82,11 @@ func (c *Conn) ReadDefaultConfigFile() error {
 	return getRadosError(int(ret))
 }
 
+// OpenIOContext creates and returns a new IOContext for the given pool.
+//
+// Implements:
+//  int rados_ioctx_create(rados_t cluster, const char *pool_name,
+//                         rados_ioctx_t *ioctx);
 func (c *Conn) OpenIOContext(pool string) (*IOContext, error) {
 	c_pool := C.CString(pool)
 	defer C.free(unsafe.Pointer(c_pool))