fix #788
improve flow
improve flow
add missing comma
miscellaneous doc improvements

* the word "system" can be misleading, so use a clearer choice of words
* reduce repetition
* mention Debian, since it is similar to Ubuntu, and is major enough
* it is now "Ubuntu", not "Ubuntu Linux"
fix #747
Merge pull request #797 from tshepang/issue788

fix #788
Merge pull request #799 from tshepang/comma

add missing comma
Merge pull request #800 from tshepang/flow2

improve flow
Merge pull request #801 from tshepang/flow

improve flow (some more)
Merge pull request #802 from tshepang/clarity

miscellaneous doc improvements
Merge pull request #803 from tshepang/link

fix #747
Merge pull request #805 from tshepang/master

make example links clickable, for convenience
point to the sources of the wiki tutorials in just one location; fix #763

* This avoids having to update the link multiple times.
* Also, mention their location, in case user has Pyramid checkout.