Provide full usage guidance

src/bin/sfembed

@@ -8,7 +8,19 @@ shellfu import pretty
 #
 
 usage() {
-    mkusage "script"
+    mkusage "$@" "[options] SCRIPT" \
+        -- \
+        "Run SCRIPT, see what it would load and print its 'portable'"     \
+        "version, ie. with those modules embedded inside."                \
+        -o \
+            "-v     enable verbose output"                                \
+            "-d     enable debugging output"                              \
+        -- \
+        "WARNING: sfembed is highly experimental, probably dangerous and" \
+        "does not always work (namely, if module loading is dynamic)."    \
+        -- \
+        "Calling sfembed WILL RUN provided SCRIPT (with no arguments);"   \
+        "currently that's how it finds out what the SCRIPT would need."
 }
 
 chk_applicable() {
@@ -115,11 +127,11 @@ main() {
     while true; do case "$1" in
         -d) PRETTY_DEBUG=true; shift ;;
         -v) PRETTY_VERBOSE=true; shift ;;
-        -*) usage ;;
+        -*) usage -w "unknown argument: $1" ;;
         *)  break ;;
     esac done
     Script="$1"
-    test -n "$Script" || usage
+    test -n "$Script" || usage -w "no SCRIPT?"
     test -f "$Script" || die "no such file: $Script"
     test -r "$Script" || die "cannot read: $Script"
     chk_applicable "$Script" || die "not applicable for embedding: $Script"