docs: expand netupgrade usage and configuration docs

Update the README with installation, requirements, supported actions, config format, and usage details. Align the CLI help text with current behavior and add startup checks for required runtime dependencies.

bin/netupgrade

@@ -1,12 +1,20 @@
 #!/bin/bash
 
 showHelp() {
-	echo "netupgrade [-f] [-y] [configfilename]"
+	echo "netupgrade [--help] [-f] [-y] [configfilename]"
 	echo ""
-	echo "              -f : Select all nodes"
-	echo "              -y : No confirmation"
-	echo "              -b : Breack on error"
-	echo "  configfilename : a cfg filename"
+	echo "  --help         Show this help message"
+	echo "  -f             Select all nodes"
+	echo "  -y             No confirmation for supported package managers"
+	echo "  configfilename Path to a cfg file"
+}
+
+checkDependencies() {
+	command -v ssh >/dev/null 2>&1 || { echo "Error: ssh is required"; exit 1; }
+	command -v whiptail >/dev/null 2>&1 || { echo "Error: whiptail is required"; exit 1; }
+	command -v nano >/dev/null 2>&1 || { echo "Error: nano is required"; exit 1; }
+	command -v sed >/dev/null 2>&1 || { echo "Error: sed is required"; exit 1; }
+	command -v tee >/dev/null 2>&1 || { echo "Error: tee is required"; exit 1; }
 }
 
 pressAnyKey(){
@@ -238,6 +246,7 @@ while [[ ${#} -gt 0 ]]; do
 	esac
 done
 
+checkDependencies
 loadConfig
 selectNodes