Documentation: block: cmdline-partition.txt fixes and additions

Make the description of the kernel command line option "blkdevparts"
a bit more flowing and readable.

Fix a few typos.
Add the optional <size> and <offset> suffixes.
Note that size can be "-" to indicate all of the remaining space.
Signed-off-by: NRandy Dunlap <rdunlap@infradead.org>
Cc: Cai Zhiyong <caizhiyong@huawei.com>
Signed-off-by: NJonathan Corbet <corbet@lwn.net>

Documentation/block/cmdline-partition.txt

 Embedded device command line partition parsing
 =====================================================================
 
-Support for reading the block device partition table from the command line.
+The "blkdevparts" command line option adds support for reading the
+block device partition table from the kernel command line.
+
 It is typically used for fixed block (eMMC) embedded devices.
 It has no MBR, so saves storage space. Bootloader can be easily accessed
 by absolute address of data on the block device.
@@ -14,22 +16,27 @@ blkdevparts=<blkdev-def>[;<blkdev-def>]
     <partdef> := <size>[@<offset>](part-name)
 
 <blkdev-id>
-    block device disk name, embedded device used fixed block device,
-    it's disk name also fixed. such as: mmcblk0, mmcblk1, mmcblk0boot0.
+    block device disk name. Embedded device uses fixed block device.
+    Its disk name is also fixed, such as: mmcblk0, mmcblk1, mmcblk0boot0.
 
 <size>
     partition size, in bytes, such as: 512, 1m, 1G.
+    size may contain an optional suffix of (upper or lower case):
+      K, M, G, T, P, E.
+    "-" is used to denote all remaining space.
 
 <offset>
     partition start address, in bytes.
+    offset may contain an optional suffix of (upper or lower case):
+      K, M, G, T, P, E.
 
 (part-name)
-    partition name, kernel send uevent with "PARTNAME". application can create
-    a link to block device partition with the name "PARTNAME".
-    user space application can access partition by partition name.
+    partition name. Kernel sends uevent with "PARTNAME". Application can
+    create a link to block device partition with the name "PARTNAME".
+    User space application can access partition by partition name.
 
 Example:
-    eMMC disk name is "mmcblk0" and "mmcblk0boot0"
+    eMMC disk names are "mmcblk0" and "mmcblk0boot0".
 
   bootargs:
     'blkdevparts=mmcblk0:1G(data0),1G(data1),-;mmcblk0boot0:1m(boot),-(kernel)'