Update README.md

Author: rahulan-c

README.md

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-# di-workflow
+# Distributional impacts analysis for rail schemes.
+
+The code in this repository is intended to support distributional impacts analysis (DIA) of the user benefits of rail schemes modelled with MOIRA or MOIRA2, in line with DfT Transport Analysis Guidance (TAG) - specifically section 2.4 (pp. 20-23) in [TAG Unit A4.2](https://www.gov.uk/government/publications/tag-unit-a4-2-distributional-impact-appraisal).
+
+A worked example is described in **workflow.qmd**.