add form to edit employee

Reviewed-on: #23
Reviewed-by: Get in my car i have candy <huydw@proton.me>

src/app/services/employee-api.service.ts

@@ -23,4 +23,8 @@ export default class EmployeeApiService {
   public create(employee: Employee) {
     return this.http.post<Employee>(`${EmployeeApiService.BASE_URL}/employees`, employee)
   }
+
+  public update(employee: Employee, id: number) {
+    return this.http.patch(`${EmployeeApiService.BASE_URL}/employees/${id}`, employee)
+  }
 }