Proposed documentation for nqp::nativecallrefresh

After discussion in #perl6.

Author: Xliff

docs/ops.markdown

@@ -2272,9 +2272,13 @@ an integral number of seconds, `_n` returns a fractional amount.
 
 ## x_posixerrno
 * `x_posixerrno()`
+* 
 
 Returns an int that corresponds to the value of POSIX's errno.
 
+## nativecallsrefresh
+Refresh the C-based data backing the Perl 6 object. This op should only be used if the user knows that changes have been made to the C-data, but these changes are not being reflected in the Perl 6 object.
+
 # <a id="async"></a> Asynchronous Operations
 
 The various asynchronous operations, such as timers and asynchronous I/O, take