doc: change line length limit in contributors guide

The DPDK documentation guidelines state that lines should be wrapped as
follows:

* The recommended style for the DPDK documentation is to put sentences on
  separate lines. This allows for easier reviewing of patches. ...
* Long sentences should be wrapped at 120 characters +/- 10 characters.
  They should be wrapped at words.

  http://dpdk.org/doc/guides/contributing/documentation.html#line-length

However, in practice, users almost never submit doc patches in this format.
Instead most users wrap their doc patches at 80 characters.

This patch updates the documentation contributors guide to reflect this
as the recommended guideline.

Signed-off-by: John McNamara <john.mcnamara@intel.com>
Reviewed-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
Reviewed-by: Shreyansh Jain <shreyansh.jain@nxp.com>

doc/guides/contributing/documentation.rst

@@ -282,33 +282,21 @@ The additional guidelines below reiterate or expand upon those guidelines.
 Line Length
 ~~~~~~~~~~~
 
-* The recommended style for the DPDK documentation is to put sentences on separate lines.
-  This allows for easier reviewing of patches.
-  Multiple sentences which are not separated by a blank line are joined automatically into paragraphs, for example::
+* Lines in sentences should be less than 80 characters and wrapped at
+  words. Multiple sentences which are not separated by a blank line are joined
+  automatically into paragraphs.
 
-     Here is an example sentence.
-     Long sentences over the limit shown below can be wrapped onto
-     a new line.
-     These three sentences will be joined into the same paragraph.
+* Lines in literal blocks **must** be less than 80 characters since
+  they are not wrapped by the document formatters and can exceed the page width
+  in PDF documents.
 
-     This is a new paragraph, since it is separated from the
-     previous paragraph by a blank line.
+  Long literal command lines can be shown wrapped with backslashes. For
+  example::
 
-  This would be rendered as follows:
-
-     *Here is an example sentence.
-     Long sentences over the limit shown below can be wrapped onto
-     a new line.
-     These three sentences will be joined into the same paragraph.*
-
-     *This is a new paragraph, since it is separated from the
-     previous paragraph by a blank line.*
-
-
-* Long sentences should be wrapped at 120 characters +/- 10 characters. They should be wrapped at words.
-
-* Lines in literal blocks must by less than 80 characters since they aren't wrapped by the document formatters
-  and can exceed the page width in PDF documents.
+     testpmd -l 2-3 -n 4 \
+             --vdev=virtio_user0,path=/dev/vhost-net,queues=2,queue_size=1024 \
+             -- -i --txqflags=0x0 --disable-hw-vlan --enable-lro \
+             --enable-rx-cksum --txq=2 --rxq=2 --rxd=1024  --txd=1024
 
 
 Whitespace