Reword elf to big error

See #397 (comment)

Author: MabezDev

espflash/src/error.rs

@@ -46,7 +46,7 @@ pub enum Error {
     )]
     #[diagnostic(
         code(espflash::image_too_big),
-        help("Reduce the size of the binary or increase the size of the partition."),
+        help("Reduce the size of the binary or increase the size of the app partition."),
         url("https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-guides/partition-tables.html#built-in-partition-tables")
     )]
     ElfTooBig(u32, u32),