Update 'Initial Soil Conditions' subsection of the 'Soil Parameters' section of the user guide

[soaressgabriel]

Description and context

• It is necessary to add more theoretical information and detail related calculations in the subsection 'Initial Soil Conditions' of the 'Soil Parameters' section of the User Guide page to better inform the user.

Proposed solution

• Update text of the 'Initial Soil Conditions' subsection of the 'Soil Parameters' section of the User Guide page with necessary changes.

Alternative solutions

N/A

Remarks

Contributors: @LINAMARIAOSORIO and Prof. Arisvaldo.