Fixed evict-leader-scheduler syntax (#3687)
Fixed evict-leader-scheduler syntax (#3687)

```
root@tidb-tools:~# pd-ctl -u my-cluster-pd.poc.svc:2379 scheduler add evict-leader-scheduler-1
add a scheduler

Usage:
  add [command]

Available Commands:
  balance-adjacent-region-scheduler add a scheduler to disperse adjacent regions on each store
  balance-hot-region-scheduler      add a scheduler to balance hot regions between stores
  balance-leader-scheduler          add a scheduler to balance leaders between stores
  balance-region-scheduler          add a scheduler to balance regions between stores
  evict-leader-scheduler            add a scheduler to evict leader from a store
  grant-leader-scheduler            add a scheduler to grant leader to a store
  label-scheduler                   add a scheduler to schedule regions according to the label
  random-merge-scheduler            add a scheduler to merge regions randomly
  scatter-range                     add a scheduler to scatter range
  shuffle-hot-region-scheduler      add a scheduler to shuffle hot regions
  shuffle-leader-scheduler          add a scheduler to shuffle leaders between stores
  shuffle-region-scheduler          add a scheduler to shuffle regions between stores

Use "help add [command] " for more information about a command.
```

```
root@tidb-tools:~# pd-ctl -u my-cluster-pd.poc.svc:2379 scheduler add evict-leader-scheduler 1
Success!
```

Co-authored-by: TomShawn <3d0966147538bc5ab020e8dffa2c0b746f9728a6@users.noreply.github.com>
pingcap/docs,pingcap/docs,pingcap/docs