site/docs: regenerate static website using Hugo

For now it's manual:

$ cd site
$ rm -rf docs/*
$ hugo

I will explore making this automatic using a GitHub Action.

site/docs/impact-evaluation-data-source/impact-evaluation-data-source.txt

@@ -0,0 +1,7 @@
+Data by scheme / tool under evaluation
+Geospatial data layers
+Independent researcher data
+Intergovernmental data (World Bank, UN, FAO data)
+National Statistics - national government data
+Other
+Private company data