Fix minor typos and update marketing copy.

Correct spelling mistakes in the AUTHORS and DISCLAIMER files, and
update the README.markdown file to credit Illumos and mention that
the ZPL is finished.

The README.markdown file is also the first impression for a handful
of new users that discover ZoL through a web search because it
doubles as the splash page for the Github repository. The build blurbs
are therefore removed because these people should be encouraged to
visit the regular home page before installing the product.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #1366

README.markdown

@@ -1,17 +1,10 @@
-Native ZFS for Linux! ZFS is an advanced file system and volume manager
-which was originally developed for Solaris. It has been successfully 
-ported to FreeBSD and now there is a functional Linux ZFS kernel port
-too. The port currently includes a fully functional and stable SPA, DMU,
-and ZVOL with a ZFS Posix Layer (ZPL) on the way!
+Native ZFS for Linux!
 
-    $ ./configure
-    $ make pkg
+ZFS is an advanced file system and volume manager which was originally
+developed for Solaris and is now maintained by the Illumos community.
 
-To copy the kernel code inside your kernel source tree for builtin
-compilation:
+ZFS on Linux, which is also known as ZoL, is currently feature complete.  It
+includes fully functional and stable SPA, DMU, ZVOL, and ZPL layers.
 
-    $ ./configure --enable-linux-builtin --with-linux=/usr/src/linux-...
-    $ ./copy-builtin /usr/src/linux-...
-
-Full documentation for building, configuring, and using ZFS can be
-found at: <http://zfsonlinux.org>
+Full documentation for installing ZoL on your favorite Linux distribution can
+be found at: <http://zfsonlinux.org>