add pigz in comment among possible values for compression type

refs https://github.com/k0lter/autopostgresqlbackup/issues/3

autopostgresqlbackup

@@ -80,7 +80,7 @@ BRWEEKLY=5
 # Default is 12 months
 BRMONTHLY=12
 
-# Choose Compression type. (gzip, bzip2, xz or zstd)
+# Choose Compression type. (gzip, pigz, bzip2, xz or zstd)
 COMP=gzip
 
 # Compression options