Fix for DebuggingNewlib wiki page

[Gene Smith]

I found an error on the page 
https://devel.rtems.org/wiki/Debugging/Newlib and would like to offer 
some suggestion to make this very useful procedure a bit clearer.

Before the line that reads

"To make the source code available to the debugger you need to unpack 
the Newlib source used by the RSB and you need to tell the debugger 
where find it."

I suggest adding a paragraph something like this:

"Take note of the number of "../" levels in the source path above. In 
this example there are six. This can vary depending on build environment."

(Note: For me the number of levels is 7.)

This series of commands need to have a "cd src" step added (this fixes 
the error):

$ cd /opt/work/chris/rtems
$ mkdir src
$ cd src
$ tar zxf 
/opt/work/chris/rtems/rsb/rtems-source-builder.git/rtems/sources/newlib-2.4.0.20160527.tar.gz

I suggesting changing this

"Create the internal work directories GCC had when the source was built. 
You can see these in the path as ../../../../../..:"

to this:

"Create dummy internal work directories like GCC had when Newlib was 
built. This is the number of levels that were noted above that you can 
see in the source path as the leading series of "../" (six in this 
example, but this can vary depending on your build environment):"

-gene