Document default video codec

Mention the default option value, like for other commands.

app/scrcpy.1

@@ -29,6 +29,8 @@ Default is 8000000.
 .BI "\-\-codec " name
 Select a video codec (h264, h265 or av1).
 
+Default is h264.
+
 .TP
 .BI "\-\-codec\-options " key\fR[:\fItype\fR]=\fIvalue\fR[,...]
 Set a list of comma-separated key:type=value options for the device encoder.

app/src/cli.c

@@ -110,7 +110,8 @@ static const struct sc_option options[] = {
         .longopt_id = OPT_CODEC,
         .longopt = "codec",
         .argdesc = "name",
-        .text = "Select a video codec (h264, h265 or av1).",
+        .text = "Select a video codec (h264, h265 or av1).\n"
+                "Default is h264.",
     },
     {
         .longopt_id = OPT_CODEC_OPTIONS,