user-search.txt: Do not format description of 'footer' operator as footer
user-search.txt: Do not format description of 'footer' operator as footer

'[[footer]]' intended to add an anchor with the name 'footer' to the
section where the 'footer' operator is described, but it actually marked
this paragraph as site footer, which resulted in an unwanted
(unreadable) coloring (see https://imgur.com/a/iyUKWyd). To fix this use
a different name for the anchor: footer-operator

Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>
Change-Id: I91c6c6b719700d7e4763577b690de1f93511472e

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