Update newly added CLMU technote section with indoor humidity and air-conditioning dehumidification

(Please see our [contribution guidelines for documentation](https://escomp.github.io/CTSM/users_guide/working-with-documentation/docs-intro.html#contribution-guidelines).)

### What sort(s) of documentation issue is this?
- [x] Something is missing and/or needs updating.

### What part(s) of the documentation does this concern?
- [x] [Technical Note](https://escomp.github.io/CTSM/tech_note/index.html) (science and design of the model)
- [ ] [User's Guide](https://escomp.github.io/CTSM/users_guide/index.html) (using the model and related tools)

### Describe the issue

Copied from #4164:

The code changes add indoor humidity and air-conditioning dehumidification to the CLMU BEM. It prognoses indoor specific humidity, calculates sensible cooling and latent dehumidification loads, and diagnoses condensate production and routes the condensate into urban runoff. The behavior is controlled by an integer CLM namelist variable, building_humidity_mode:

- 0: use the existing CLMU formulation without indoor humidity or AC dehumidification;
- 1: enable indoor humidity and latent heat exchange, but no AC dehumidification (requires prognostic building temperature, building_temp_method=1); and
- 2: enable indoor humidity, latent heat exchange, dehumidification load, and condensate production (requires prognostic building temperature, urban_hac to be ON or ON_WASTEHEAT and urban_explicit_ac=.true.).

The default is set to 0 to ensure bit-for-bit reproducibility with the original scheme.

### Additional context (optional)
Currently blocked by #4179.