Add project and group notification settings info

Notification settings are described but aren't mentioned where they are or where to change them.

Thanks @cpallares! :D

2 simple things:

• Pls add the images to the img folder under the same dir your markdown file is (feel free to create one if necessary)
• Pls use _ instead of - in the urls :)

https://docs.gitlab.com/ce/development/doc_styleguide.html

assigned to @cpallares

added ~15078 docs-review labels

added 1 commit

• 20aab3c8 - Add project and group notification settings info

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assigned to @marcia

Thanks @marcia :)

approved this merge request

Thank you @cpallares

merged

mentioned in commit 010a9c6b