User's Guide: Creating sparse-grid mesh and surface files

> Once again @swensosc has fixed sparse-grid issues.
>
> He made a mesh file and surface dataset that work!
>
> mesh: /glade/work/afoster/ABoVE/for_adrianna/ESMFmesh_ctsm_NWT_pts.nc
> surface file: /glade/work/afoster/ABoVE/for_adrianna/surfdata_0.9x1.25_hist_2000_16pfts_c250502.nc
>
> Here are instructions:
>
> ```
> 1) use create_esmf_mesh_sites.py to create a mesh including only desired site coordinates
>
> 2) create surface data file in tools/mksurfdata_esmf
>
> ./gen_mksurfdata_namelist --start-year 2000 --end-year 2000 --res 0.9x1.25 --model-mesh ESMFmesh_ctsm_NWT_pts.nc --model-mesh-nx 9 --model-mesh-ny 1
>
> ./gen_mksurfdata_jobscript_single --number-of-nodes 1 --tasks-per-node 9 --namelist-file surfdata_0.9x1.25_hist_2000_78pfts_c250502.namelist
>
> 3) use mesh with subset_datm_vector.py to create datm forcing files
>
> ```
>
> With his script I also made a DATM mesh file that is working as well!
>
> /glade/work/afoster/ABoVE/for_adrianna/ABoVE_nwt_datmclmforc.GSWP3.c2011.0.5x0.5.TPQWL.SCRIP.210520_ESMFmesh.NWT_pts.nc
>
> Thank you @swensosc!
>
> @ekluzek are still not sure why this set of files work and the case described above doesn't.

_Originally posted by @adrifoster in [#3099](https://github.com/ESCOMP/CTSM/issues/3099#issuecomment-2848333068)_