Fix misleading text on referrers admin screen

The help text on the left of the "Manage Referrers" screen is incorrect and misleading. It tells you to turn the "Record External Referrers" option ON to prevent the recording of referrers. In fact, you should turn the option off. The text also says that the default value is "OFF', but I think the default is "ON".

The text also does not mention the second option that allows you to prevent the display of the referrers while retaining the ability to record the referrers.

Suggested help text for the screen:

Record External Referrers:
Turn this option off if you want to prevent Confluence from recording the external URLs that link to Confluence pages.

Show Referrers in Page Info:
If this option is turned on, the 'Info' screen for each page will display a section called 'Hot Referrers', showing the top 10 external links pointing to that page. Turn the option off if you want to record referrers (see above) but prevent the display of 'Hot Referrers'.

Excluded External Referrer Prefixes:
Here you can specify a list of blocked URLs. Any incoming links from URLs that match the list will no longer be recorded. Use the following characters to separate domain names: space, tab, new line, colon or semi-colon.