Update tech docs

Author: mkavulich

doc/TechDocs/ush/modules.rst

@@ -17,10 +17,10 @@ ush
    get_crontab_contents
    get_obs
    link_fix
-   mrms_pull_topofhour
    python_utils
    retrieve_data
    run_srw_tests
+   select_validtime_obs
    set_cycle_and_obs_timeinfo
    set_fv3nml_ens_stoch_seeds
    set_gridparams_ESGgrid

doc/TechDocs/ush/mrms_pull_topofhour.rst

@@ -0,0 +1,7 @@
+select\_validtime\_obs module
+=============================
+
+.. automodule:: select_validtime_obs
+   :members:
+   :undoc-members:
+   :show-inheritance: