Document the new config settings for packet search.

There are three new settings, though these are intended more to preserve
the state of the user's packet search across runs of termshark.

docs/UserGuide.md

@@ -661,6 +661,9 @@ Termshark reads options from a TOML configuration file saved in `$XDG_CONFIG_HOM
 - `recent-files` (string list) - the pcap files shown when the user clicks the "recent" button in termshark. Newly viewed files are added to the beginning.
 - `recent-filters` (string list) - recently used Wireshark display filters.
 - `respect-colorterm` (bool) - if termshark detects you are using base16-shell, it won't map any theme RGB color names (like #90FF32) to 0-21 in the 256-color space to avoid clashes with the active base16 theme. This shouldn't affect color reproduction if the terminal is 24-bit capable, but some terminal emulators (e.g. gnome-terminal) seem to use the 256-color space anyway. Termshark works around this by falling back to 256-color mode, interpolating RGB colors into the 256-color space and avoiding 0-21. If you really want termshark to run in 24-bit color mode anyway, set this to true.
+- `search-type` - (string) - how to interpret the user's packet search term; one of `filter`, `hex`, `string` or `regex`.
+- `search-target` - (string) - the type of packet data to search (unless `search-type` is `filter`); one of `list`, `details` or `bytes`.
+- `search-case-sensitive` - (bool) - true if the user's packet search should be sensitive to the case of the search term.
 - `stream-cache-size` (int) - termshark caches the structures and UI used to display reassembled TCP and UDP streams. This allows for quickly redisplaying a stream that's been loaded before. This setting determines how many streams are cached. The default is 100.
 - `stream-view` (string - the default view when displaying a reassembled stream. Choose from "hex"/"ascii"/"raw".
 - `suppress-tshark-errors` (bool) - if `true`, hide from the UI any errors generated during parsing of tshark-generated XML.