change the default term to `foot`

it is closer to the suckless philosophy (foot implements things that the suckless
guys would say that should be done by tmux or something else, but I have no
desire to create a new terminal emulator, and the best fit is foot)

also alacritty uses +100Mb of memory, more that dwl itself (~90Mb)
and foot only ~20Mb

config.def.h

@@ -98,7 +98,7 @@ static const double accel_speed = 0.0;
 #define SHCMD(cmd) { .v = (const char*[]){ "/bin/sh", "-c", cmd, NULL } }
 
 /* commands */
-static const char *termcmd[] = { "alacritty", NULL };
+static const char *termcmd[] = { "foot", NULL };
 static const char *menucmd[] = { "bemenu-run", NULL };
 
 static const Key keys[] = {