ifcclash ifccsv ifcdiff ifcpatch: README.md stubs

The pyproject.toml files were referencing these missing files

src/ifcclash/README.md

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+# IfcClash
+
+IFC clash detection library to handle intersections, collisions, and clearance checks between building elements in IFC models.
+
+## Features
+
+- **Multiple detection modes**: intersection, collision, and clearance checking
+- **Flexible clash sets**: Compare elements within a single model or between multiple IFC files
+- **Smart grouping**: Automatically group related clashes
+- **Export options**: Export clash results to BCF-XML or JSON formats
+- **Element filtering**: Use selectors to specify which elements to check for clashes