mkdocs.yml: Added path to "software_architecture.md" file for cost_estimation

mkdocs.yml

@@ -285,6 +285,7 @@ nav:                                      # Customizes the main navigation struc
             - Getting Started: documentation/analysis/cost_estimation/getting_started.md
             - Methods: documentation/analysis/cost_estimation/operating_cost_method.md
             - Run your First Estimation: documentation/analysis/cost_estimation/run_your_first_cost_estimation.md
+            - Software Architecture: documentation/analysis/cost_estimation/software_architecture.md
             # - API Reference: # TODO define for Python
           - Ecological Assessment:
             - Introduction: documentation/analysis/ecological_assessment/index.md