Debian install docs issues

The install instructions on https://www.pgcli.com/install don't match the install instructions on this repo's readme. On this repo it lists the dependencies as:

```
sudo apt-get install python-dev libpq-dev libevent-dev
```

on the website it lists the dependencies as:

```
sudo apt-get install libpq-dev python-dev # debian
```

Also when I try to install `python-dev` I get this error which I resolved by moving to `python-dev-is-python3`:

```
apt install python-dev
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package python-dev is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source
However the following packages replace it:
python-dev-is-python3

E: Package 'python-dev' has no installation candidate
```

Aside from these minor issues the tool is great and thank you for it!

リポジトリのREADMEにあるDebianの依存関係コマンドと、https://www.pgcli.com/install のインストール手順を比較し、その後、issueに記載されている現在のDebianパッケージ名を確認します。両方のドキュメントの場所で、一貫性があり動作するDebianのインストール手順が示されれば、作業は完了です。

索引モデルが issue の本文から書いたものです。