Accept Cmd as shortcut modifier

In addition to (left) Alt, also accept (left) Cmd. This is especially
convenient for macOS users.

README.md

@@ -572,7 +572,7 @@ Also see [issue #14].
 ## Shortcuts
 
 In the following list, `MOD` is the shortcut modifier. By default, it's (left)
-`Alt`.
+`Alt` or (left) `Cmd`.
 
 It can be changed using `--shortcut-mod`. Possible keys are `lctrl`, `rctrl`,
 `lalt`, `ralt`, `lcmd` and `rcmd`. For example:

app/scrcpy.1

@@ -157,7 +157,7 @@ A shortcut can consist in several keys, separated by '+'. Several shortcuts can
 
 For example, to use either LCtrl+LAlt or LCmd for scrcpy shortcuts, pass "lctrl+lalt,lcmd".
 
-Default is "lalt" (left-Alt).
+Default is "lalt,lcmd" (left-Alt or left-Cmd).
 
 .TP
 .B \-S, \-\-turn\-screen\-off
@@ -218,7 +218,7 @@ Default is 0 (automatic).\n
 .SH SHORTCUTS
 
 In the following list, MOD is the shortcut modifier. By default, it's (left)
-Alt, but it can be configured by \-\-shortcut-mod.
+Alt or (left) Cmd, but it can be configured by \-\-shortcut-mod.
 
 .TP
 .B MOD+f

app/src/cli.c

@@ -149,7 +149,7 @@ scrcpy_print_usage(const char *arg0) {
         "        For example, to use either LCtrl+LAlt or LCmd for scrcpy\n"
         "        shortcuts, pass \"lctrl+lalt,lcmd\".\n"
         "\n"
-        "        Default is \"lalt\" (left-Alt).\n"
+        "        Default is \"lalt,lcmd\" (left-Alt or left-Cmd).\n"
         "\n"
         "    -S, --turn-screen-off\n"
         "        Turn the device screen off immediately.\n"
@@ -199,7 +199,8 @@ scrcpy_print_usage(const char *arg0) {
         "Shortcuts:\n"
         "\n"
         "    In the following list, MOD is the shortcut modifier. By default,\n"
-        "    it's (left) Alt, but it can be configured by --shortcut-mod.\n"
+        "    it's (left) Alt or (left) Cmd, but it can be configured by\n"
+        "    --shortcut-mod.\n"
         "\n"
         "    MOD+f\n"
         "        Switch fullscreen mode\n"

app/src/scrcpy.h

@@ -95,8 +95,8 @@ struct scrcpy_options {
         .last = DEFAULT_LOCAL_PORT_RANGE_LAST, \
     }, \
     .shortcut_mods = { \
-        .data = {SC_MOD_LALT}, \
-        .count = 1, \
+        .data = {SC_MOD_LALT, SC_MOD_LCMD}, \
+        .count = 2, \
     }, \
     .max_size = DEFAULT_MAX_SIZE, \
     .bit_rate = DEFAULT_BIT_RATE, \