`infra/README.md`: セットアップ後の確認事項の整備

[argondev22]

強化項目

• AWSの設定
• echo $SHELL
• age-keygen -y ~/.config/age/age.key

参照: https://github.com/argon-dev22/environments/tree/main/infra#5-%E3%82%BB%E3%83%83%E3%83%88%E3%82%A2%E3%83%83%E3%83%97%E5%BE%8C%E3%81%AE%E7%A2%BA%E8%AA%8D

追加: 下記の表示は正常なのか？

- zsh-users/zsh-completions: not installed
- zdharma-continuum/history-search-multi-word: not installed
- zsh-users/zsh-autosuggestions: not installed
- zdharma-continuum/fast-syntax-highlighting: not installed
- themes/pmcgee: not installed
[zplug] Start to install 5 plugins in parallel

 ✔  Installed!            zsh-users/zsh-completions
 ✔  Installed!            zdharma-continuum/history-search-multi-word
 ✔  Installed!            zsh-users/zsh-autosuggestions
 ✔  Installed!            zdharma-continuum/fast-syntax-highlighting
 ✔  Installed!            themes/pmcgee

[zplug] Elapsed time: 2.4396 sec.
 ==> Installation finished successfully!