homework: default to btrfs compression

This follows what Fedora did with 34: enables compression by default,
lowering IO bandwidth and reducing disk space use, at the price of
slightly higher CPU use.

https://fedoraproject.org/wiki/Changes/BtrfsTransparentCompression

src/home/homework-mount.c

@@ -25,7 +25,7 @@ static const char *mount_options_for_fstype(const char *fstype) {
         if (streq(fstype, "xfs"))
                 return "noquota";
         if (streq(fstype, "btrfs"))
-                return "noacl";
+                return "noacl,compress=zstd:1";
         return NULL;
 }