add set_options link to FAQ on metadata (#6056)
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
pydata/xarray,markelg/xray,jhamman/xarray,jhamman/xarray,pydata/xarray,markelg/xray,jhamman/xarray,pydata/xarray,markelg/xray