Clarify that chunker sizes are in bytes

Clarify that the Rabin fingerprint chunker is in bytes, and recommend
using larger chunk sizes than shown in the provided examples.

People are getting confused over chunker sizes and incorrectly assuming
they're in kiB and not bytes.

core/commands/add.go

@@ -78,12 +78,16 @@ You can now refer to the added file in a gateway, like so:
 
 The chunker option, '-s', specifies the chunking strategy that dictates
 how to break files into blocks. Blocks with same content can
-be deduplicated. The default is a fixed block size of
+be deduplicated. Different chunking strategies will produce different
+hashes for the same file. The default is a fixed block size of
 256 * 1024 bytes, 'size-262144'. Alternatively, you can use the
-rabin chunker for content defined chunking by specifying
-rabin-[min]-[avg]-[max] (where min/avg/max refer to the resulting
-chunk sizes). Using other chunking strategies will produce
-different hashes for the same file.
+Rabin fingerprint chunker for content defined chunking by specifying
+rabin-[min]-[avg]-[max] (where min/avg/max refer to the desired
+chunk sizes in bytes), e.g. 'rabin-262144-524288-1048576'.
+
+The following examples use very small byte sizes to demonstrate the
+properties of the different chunkers on a small file. You'll likely
+want to use a 1024 times larger chunk sizes for most files.
 
   > ipfs add --chunker=size-2048 ipfs-logo.svg
   added QmafrLBfzRLV4XSH1XcaMMeaXEUhDJjmtDfsYU95TrWG87 ipfs-logo.svg