Add a small note about long term data preservation

[blakesweeney]

This is required by the EBI. Adding it next to the license seems reasonable.

[carlosribas]

I wonder whether or not we need to add a note to the sequence search help page. On this page we say that data is stored for only seven days

[blakesweeney]

Good point, I didn't think of that. I think the sequence searches that are done and the data in RNAcentral are different things so we only need to label RNAcentral data. I can bring it up at the next SCF meeting though.

[carlosribas]

I agree, but from the user's point of view there is no such difference :)
Other than that, we can merge this code.