feat: ウェルカムメッセージを更新する

[MikuroXina]

Type of Change:

機能の変更, データの修正

Details of implementation (実施内容)

ウェルカムメッセージの Getting Started がリンク切れしていたので, Notion に移行していたものへリンクを貼り直しました.

また, メンバー情報登録ウェブアプリへの誘導がちょっと不十分だったので, そこへのリンクを追加しました.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 58.97%. Comparing base (23b5909) to head (a90773b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1296   +/-   ##
=======================================
  Coverage   58.97%   58.97%           
=======================================
  Files         112      112           
  Lines        7322     7322           
  Branches      530      530           
=======================================
  Hits         4318     4318           
  Misses       2475     2475           
  Partials      529      529           

Flag	Coverage Δ
unittests	58.97% <100.00%> (ø)

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