Specify :okwarning: as an option in the ipython:: block to suppress a warning

[orbeckst]

CI suggests to filter warnings:

WARNING: 
>>>-------------------------------------------------------------------------
Warning in /home/runner/work/UserGuide/UserGuide/doc/source/reading_and_writing.rst at block ending on line 225
Specify :okwarning: as an option in the ipython:: block to suppress this message
----------------------------------------------------------------------------
/home/runner/micromamba/envs/mda-user-guide/lib/python3.10/site-packages/MDAnalysis/coordinates/DCD.py:165: DeprecationWarning: DCDReader currently makes independent timesteps by copying self.ts while other readers update self.ts inplace. This behavior will be changed in 3.0 to be the same as other readers. Read more at https://github.com/MDAnalysis/mdanalysis/issues/3889 to learn if this change in behavior might affect you.
  warnings.warn("DCDReader currently makes independent timesteps"
<<<-------------------------------------------------------------------------
WARNING: 
>>>-------------------------------------------------------------------------
Warning in <rst_epilog> at block ending on line 1
Specify :okwarning: as an option in the ipython:: block to suppress this message
----------------------------------------------------------------------------
/home/runner/micromamba/envs/mda-user-guide/lib/python3.10/site-packages/MDAnalysis/coordinates/DCD.py:165: DeprecationWarning: DCDReader currently makes independent timesteps by copying self.ts while other readers update self.ts inplace. This behavior will be changed in 3.0 to be the same as other readers. Read more at https://github.com/MDAnalysis/mdanalysis/issues/3889 to learn if this change in behavior might affect you.
  warnings.warn("DCDReader currently makes independent timesteps"
<<<-------------------------------------------------------------------------