Update README.md

Author: lrnv

README.md

@@ -21,6 +21,6 @@ Todo :
 - [x] Add non-HMD rate tables from R packages, whith the same interface. 
 - [x] Life tables with covariates (country is already somewhat of a covariate..)
 - [x] Life random variables
-- [ ] better proofness to poor inputs (e.g. return missings ? return errors?)
-- [ ] better docs
-- [ ] better tests
+- [x] better proofness to poor inputs (e.g. return missings ? return errors?)
+- [ ] improve docs
+- [ ] improve tests