docs: i2c: smbus-protocol: improve I2C Block transactions description

Clarify from the beginning what these transactions are, and specifically
how they differ from the SMBus counterparts, i.e. the lack of a Count byte.

Signed-off-by: Luca Ceresoli <luca@lucaceresoli.net>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>

Documentation/i2c/smbus-protocol.rst

@@ -282,9 +282,10 @@ This is implemented the following way in the Linux kernel:
 I2C Block Transactions
 ======================
 
-The following I2C block transactions are supported by the
-SMBus layer and are described here for completeness.
-They are *NOT* defined by the SMBus specification.
+The following I2C block transactions are similar to the SMBus Block Read
+and Write operations, except these do not have a Count byte. They are
+supported by the SMBus layer and are described here for completeness, but
+they are *NOT* defined by the SMBus specification.
 
 I2C block transactions do not limit the number of bytes transferred
 but the SMBus layer places a limit of 32 bytes.