/usr/lib/ghc-doc/hoogle/notmuch-web.txt is in libghc-notmuch-web-doc 0.2.0-1build1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/ghc-doc/hoogle/../../../share/doc/libghc-notmuch-web-doc/html/notmuch-web.txt