nginx: normalize installation (docs and script)s over all distros

This is the revision of the documentation about the varous nginx installation
variants.  It also implements the nginx installation scripts for morty and
filtron.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

utils/searx.sh

@@ -114,9 +114,7 @@ usage() {
 
     # shellcheck disable=SC1117
     cat <<EOF
-
 usage::
-
   $(basename "$0") shell
   $(basename "$0") install    [all|user|searx-src|pyenv|uwsgi|packages|buildhost]
   $(basename "$0") update     [searx]
@@ -178,8 +176,6 @@ EOF
 }
 
 main() {
-    rst_title "$SEARX_INSTANCE_NAME" part
-
     required_commands \
         sudo systemctl install git wget curl \
         || exit
@@ -187,9 +183,8 @@ main() {
     local _usage="unknown or missing $1 command $2"
 
     case $1 in
-        --source-only)  ;;
+        --getenv)  var="$2"; echo "${!var}"; exit 0;;
         -h|--help) usage; exit 0;;
-
         shell)
             sudo_or_exit
             interactive_shell "${SERVICE_USER}"
@@ -203,6 +198,7 @@ main() {
                 *) usage "$_usage"; exit 42;;
             esac ;;
         install)
+            rst_title "$SEARX_INSTANCE_NAME" part
             sudo_or_exit
             case $2 in
                 all) install_all ;;