Move the part of parameter description in dumpling-overview.md (#5521)

Author: Joyinqin

dumpling-overview.md

@@ -69,7 +69,7 @@ In the command above:
 + `-h`, `-p`, and `-u` respectively mean the address, the port, and the user. If a password is required for authentication, you can use `-p $YOUR_SECRET_PASSWORD` to pass the password to Dumpling.
 + `-o` specifies the export directory of the storage, which supports a local file path or a [URL of an external storage](/br/backup-and-restore-storages.md).
 + `-r` specifies the maximum number of rows in a single file. With this option specified, Dumpling enables the in-table concurrency to speed up the export and reduce the memory usage.
-+ `-F` specifies the maximum size of a single file.
++ The `-F` option is used to specify the maximum size of a single file (the unit here is `MiB`; inputs like `5GiB` or `8KB` are also acceptable). It is recommended to keep its value to 256 MiB or less if you plan to use TiDB Lightning to load this file into a TiDB instance.
 
 > **Note:**
 >
@@ -249,7 +249,6 @@ Examples:
 The exported file is stored in the `./export-<current local time>` directory by default. Commonly used options are as follows:
 
 - The `t` option specifies the number of threads for the export. Increasing the number of threads will increase the concurrency of Dumpling but will also increase the database's memory consumption. Therefore, it is not recommended to set the number too large.
-- The `-F` option is used to specify the maximum size of a single file (the unit here is `MiB`; inputs like `5GiB` or `8KB` are also acceptable). It is recommended to keep its value to 256 MiB or less if you plan to use TiDB Lightning to load this file into a TiDB instance.
 - The `-r` option specifies the maximum number of records (or the number of rows in the database) for a single file. When it is enabled, Dumpling enables concurrency in the table to improve the speed of exporting large tables.
 
 With the above options specified, Dumpling can have a quicker speed of data export.