Add explanation in self-hosted version of how can the user increase the max upload memory filesize

<img width="1227" alt="image" src=" />

Currently the user needs to see this error, know to search inside the outline repository, identify line 59 from attachments.ts that contain the error message
`

Then see line 55


To then go to the

AttachmentHelper.presetToMaxUploadSize

on line 106 to identify this


and then it will need to add either the FILE_STORAGE_IMPORT_MAX_SIZE, FILE_STORAGE_WORKSPACE_IMPORT_MAX_SIZE or FILE_STORAGE_UPLOAD_MAX_SIZE to make it work.