Show help when no arguments

Signed-off-by: Adrien Gallouët <adrien@gallouet.fr>

README.md

@@ -22,6 +22,24 @@ To build and install the latest version with [meson](http://mesonbuild.com):
 
 The more classical autotools suite is also available but not recommended.
 
+### Usage
+
+Just run `glorytun` with no arguments to view the list of available commands:
+
+```
+$ glorytun
+available commands:
+
+  show     show all running tunnels
+  bench    start a crypto bench
+  bind     start a new tunnel
+  set      change tunnel properties
+  keygen   generate a new secret key
+  path     manage paths
+  version  show version
+
+```
+
 ### Mini HowTo
 
 Glorytun does not touch network configuration of its interface,

src/main.c

@@ -69,15 +69,14 @@ main(int argc, char **argv)
         {"version", "show version", gt_version},
         {NULL}};
 
-    if (argc < 2)
-        return gt_show(argc, argv);
-
-    for (int k = 0; cmd[k].name; k++) {
-        if (!str_cmp(cmd[k].name, argv[1]))
-            return cmd[k].call(argc - 1, argv + 1);
+    if (argv[1]) {
+        for (int k = 0; cmd[k].name; k++) {
+            if (!str_cmp(cmd[k].name, argv[1]))
+                return cmd[k].call(argc - 1, argv + 1);
+        }
     }
 
-    printf("unknown command `%s', available commands:\n\n", argv[1]);
+    printf("available commands:\n\n");
 
     int len = 0;