better type annotation for genHeader

lib/libmtar.lua

@@ -31,7 +31,7 @@ local function cleanPath(path)
  return table.concat(pt,"/")
 end
 
-function mtar.genHeader(fname,len) -- generate a header for file *fname* when provided with file length *len*
+function mtar.genHeader(fname,len) -- string number -- string -- generate a header for file *fname* when provided with file length *len*
  return string.format("%s%s%s",cint(fname:len(),2),fname,cint(len,2))
 end