glossary expanded by soil moisture terms

[vgro]

This PR added definitions of different soil moisture related variables to the glossary. Please check if correct and if any important terms are missing.

Fixes #772

Type of change

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist

• Make sure you've run the pre-commit checks: $ pre-commit run -a
• All tests pass: $ poetry run pytest

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.18%. Comparing base (f0471ad) to head (7cd69a8).

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #821   +/-   ##
========================================
  Coverage    94.18%   94.18%           
========================================
  Files           74       74           
  Lines         5311     5311           
========================================
  Hits          5002     5002           
  Misses         309      309           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[lelavathy]

please check the definition:
a ratio expressing the amount of water in soil, as a percentage, compared to the total water-holding capacity between the wilting point (very dry) and saturation (very wet) for a given soil type. Expressed as a unitless ratio (0–1) or %.

formula: RSM=soil moisture-wilting point/saturation-wilting point

references:

1. https://weather.ndc.nasa.gov/sport/training/articles/20170320184849_NASA-Land-Information-System-LIS-Soil-Moisture-Percentile/media/lis-soil-moisture-quick-guide-by-nasa-sport.pdf#:~:text=Relative%20soil%20moisture%20is%20a%20ratio%20of,and%20is%20also%20expressed%20as%20a%20percentage.&text=0%2D10%20cm%20Relative%20Soil%20Moisture%20(RSM)%20(%)%2C,saturation%20points%20for%20a%20given%20soil%20type.
2. https://crops.extension.iastate.edu/post/facts-soil-moisture-benchmarking-tool

[lelavathy]

missing soil moisture terms:
1.permanent wilting point: The water content at which plants can no longer extract moisture, leading to wilting and potential plant death. Water is still present in the soil, but it is tightly bound and unavailable to plants. This is lower limit of plant-available water. Expressed in m3/m3, %, or mm

2. available water capacity: amount of water that a soil can store and make available to plants, defined as the difference between field capacity and the permanent wilting point. Expressed in m3/m3, %, or mm

3. saturation soil moisture: maximum amount of water a soil can hold when all its pores are completely filled with water — that is, the soil is fully saturated and contains no air in the pore spaces. Expressed in m3/m3, %, or mm.

reference:
1.https://www.fao.org/4/y4690e/y4690e04.htm
2.https://www.droughtmanagement.info/literature/BC_MA_Soil_Water_Storage_Capacity_2005.pdf
3.Rai, R. K., Singh, V. P., & Upadhyay, A. (2017). Planning and evaluation of irrigation projects: methods and implementation. Academic press.
4.https://connectedcrops.ca/the-ultimate-guide-to-soil-moisture/

[vgro]

@lelavathy I have updated the relative soil moisture and added the missing terms. Could you please check the changes and approve when you're happy with it :-)