Update README.md

Merge branch 'main' of https://github.com/LittleBeannie/gsDesign2 into main

ongoing updates

add tests of `fixed_design`

add tests of `utility_tbl`

update/test `check_arg`

update test tol

add tests of `tEvents`

add tests of `eEvents_df`

add tests for `eAccrual`

update `gs_design_npe` and `gs_power_ahr`

add a test of `gs_design_npe`

update `gs_design_npe`

update a test

update author list