Slightly simplify the networking README_NATIVE.md install steps

[jfingerh]

plus some minor typo corrections.

[jfingerh]

Notes on the changes:

As far as I can see, there is no variable named SCRIPT_DIR in any of the bash scripts in the ipdk/build/networking directory and its subdirectories. Thus it has no effect at all assigning a value to SCRIPT_DIR while running the install script.

It seems to me unnecessarily confusing to give instructions to clone the ipdk repo anywhere you want, and call it <CLONE-PATH>, and then the very first example of how to run the install script only works if you did it in the /git directory. It seems much less confusing to omit that option, and simply always use the -d <CLONE-PATH> in all choices shown. One less thing to get wrong for the reader.

[ffoulkes]

@n-sandeep @5abeel
Can I get your feedback / approval / disapproval for this PR?

[ffoulkes]

I think this is a typo for SCRIPTS_DIR, which is referenced in host_install.sh.