doc: Unable to upload files with allowed extensions

[MirKue]

I followed the instructions to harden my Open WebUI instance.

I ran into trouble with the section https://docs.openwebui.com/getting-started/advanced-topics/hardening/#file-upload-limits, to be more specific with RAG_ALLOWED_FILE_EXTENSIONS=.pdf,.txt,.md,.docx,.csv:

Afterwards I couldn't upload files to add them to a knowledge base and received the response body {"detail": "[ERROR: file type <extension> is not allowed]"} with different values for depending on the respective file extension. After I figured that the environment variable mentioned above might be the cause, I removed the leading dots in the list of allowed file extensions and tested the file upload successfully.

I propose to adjust the documentation accordingly.

Following the code of conduct I opened a discussion here first.