Improve log redaction example

The log redaction example would make more sense if we included the <UD> / </UD> tags in the unredacted message:

0ms [I0] {2506} [INFO] (instance - L:421) Effective connection string:

<UD>couchbase://127.0.0.1?username=Administrator&console_log_level=5&;</UD>.

Bucket=default

And perhaps add a brief explanation on how the redaction works (as in, the script searches for the tags and performs the replacement based on the tags.