chore: Update DESCRIPTION with cph

Author: mhovd

DESCRIPTION

@@ -3,7 +3,7 @@ Type: Package
 Title: Estimated Glomerular Filtration Rate (eGFR) Calculators
 Version: 0.1.0
 Authors@R: 
-    person("Markus", "Hovd", email = "markus@hovd.io", role = c("aut", "cre"))
+    person("Markus", "Hovd", email = "markus@hovd.io", role = c("aut", "cre", "cph"))
 Description: A comprehensive, vectorised toolkit for estimating glomerular
     filtration rate (eGFR) and creatinine clearance from serum creatinine,
     cystatin C, or both. Implements 20 validated adult, paediatric, and