How to add partitions to the existing table in PostgreSQL

How to add partitions to the existing table in PostgreSQL

for ex, below is my table definition:

CREATE TABLE ot.employee
(
    empno smallint NOT NULL,
    ename character varying(20),
    job character varying(20),
    deptno smallint
)

Now I would like to add partition to deptno column

I don't see any alter table command to add the partition to the existing table.

Please help me on this.