docs: Added to "known issues" section (#63)

Author: DenverCoder1

README.md

@@ -54,9 +54,11 @@ To sign the extension for use in Firefox, you will need credentials from https:/
 The following are known limitations that cannot be fixed:
 
 -   The fetched comment may occasionally be the edited version instead of the original. This is because the Pushshift archive may take more time to archive the comment than it took the user to edit the comment, therefore causing Pushshift to archive the edited version and not the original. Additionally, comments that are several years old may also show the edited version since the original versions of comments edited before the first archival will not appear in Pushshift.
--   Comments that were posted within the past few minutes may occasionally not be found since Pushshift can take some time to archive all comments.
--   Comments in private subreddits will not be found as they are not able to be archived by Pushshift.
--   Comments deleted by Reddit's spam filter will not be found as the text is never available for Pushshift to archive.
+-   Comments that were posted within the past few minutes may occasionally show "not found" since Pushshift can take some time to archive all comments.
+-   Comments in private subreddits will show "not found" as they are not able to be archived by Pushshift.
+-   Comments deleted by Reddit's spam filter will show "not found" as the text is never available for Pushshift to archive.
+-   Comments and posts by users who have requested the deletion of the data from Pushshift will show as "not found".
+-   If the Pushshift API is temporarily down or partially down, the message "fetch failed" may appear.
 
 ## Changelog