merge: Add missing IMPORTANT_NOTES.md from Sharkey/OldJoinSharkey (!443)

View MR for information: !443



Approved-by: dakkar <dakkar@thenautilus.net>
Approved-by: Amelia Yukii <amelia.yukii@shourai.de>

IMPORTANT_NOTES.md

+# Basic Precautions
+
+When using a service with Sharkey, there are several important points to keep in mind.
+
+1. Because it is decentralized, there is no guarantee that data you upload will be deleted from all other servers even if you delete it once. (However, this applies to the internet in general.)
+
+2. Even for posts made in private, there is no guarantee that the recipient's server will treat them as private in the same way. Please exercise caution when posting personal or confidential information. (Again, this applies to the internet in general.)
+
+3. Account deletion can be a resource-intensive process and may take a long time. In cases with a lot of uploaded data, it may even be impossible to delete an account.
+
+4. Please disable ad blockers. Some servers may rely on advertising revenue to cover operating costs. Additionally, ad blockers can mistakenly block content and features unrelated to ads, potentially causing issues with the client's functionality and preventing normal use of Sharkey. Therefore, we recommend turning off ad blockers and similar features when using Sharkey.
+
+Please understand these points and enjoy using the service.
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