crc32: move long comment about crc32 fundamentals to Documentation/

Move a long comment from lib/crc32.c to Documentation/crc32.txt where it
will more likely get read.

Edited the resulting document to add an explanation of the slicing-by-n
algorithm.

[djwong@us.ibm.com: minor changelog tweaks]
[akpm@linux-foundation.org: fix typo, per George]
Signed-off-by: George Spelvin <linux@horizon.com>
Signed-off-by: Bob Pearson <rpearson@systemfabricworks.com>
Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/Documentation/00-INDEX b/Documentation/00-INDEX
index a1a6432..2214f12 100644
--- a/Documentation/00-INDEX
+++ b/Documentation/00-INDEX
@@ -104,6 +104,8 @@
 	- info on CPU_IDLE, CPU idle state management subsystem.
 cputopology.txt
 	- documentation on how CPU topology info is exported via sysfs.
+crc32.txt
+	- brief tutorial on CRC computation
 cris/
 	- directory with info about Linux on CRIS architecture.
 crypto/