add gitignore to ignore .idea

[ElecTwix]

I'm not sure it is good practice to add .idea to the git repo, to point I'm making is not everyone uses JetBrains's IDEs. still can be discussed.

[LLNet]

@ElecTwix yes and it why add it to .gitignore - so users not coming to add files to repo with accident.

• https://github.com/joomla/joomla-cms/blob/4.3-dev/.gitignore#L6
• https://github.com/redCOMPONENT-COM/redCORE/blob/develop/.gitignore#L12
• https://github.com/php-mod/curl/blob/master/.gitignore#L6
• https://github.com/Laragear/Surreal/blob/master/.gitignore#L5 ( surrealdb for Laravel)