add set_options link to FAQ on metadata (#6056)

* link to xr.set_options in reference to "global flag"

* syntax fix

* switch to sphinx :py:func: anchor reference

* xarray, not xr, in internal ref

doc/getting-started-guide/faq.rst

@@ -140,12 +140,11 @@ conventions`_. (An exception is serialization to and from netCDF files.)
 
 An implication of this choice is that we do not propagate ``attrs`` through
 most operations unless explicitly flagged (some methods have a ``keep_attrs``
-option, and there is a global flag for setting this to be always True or
-False). Similarly, xarray does not check for conflicts between ``attrs`` when
-combining arrays and datasets, unless explicitly requested with the option
-``compat='identical'``. The guiding principle is that metadata should not be
-allowed to get in the way.
-
+option, and there is a global flag, accessible with :py:func:`xarray.set_options`,
+for setting this to be always True or False). Similarly, xarray does not check
+for conflicts between ``attrs`` when combining arrays and datasets, unless
+explicitly requested with the option ``compat='identical'``. The guiding
+principle is that metadata should not be allowed to get in the way.
 
 What other netCDF related Python libraries should I know about?
 ---------------------------------------------------------------