Minor changes and typos

[martinosorb]

A few minor changes:

• In the index's introductory explanation there were at least a couple of typos. Fixes #326.
• The same introduction had some unclear 'etc.' and less polished language that I edited.
• Braces are not usually called "squiggle braces". I Googled this expression and it's essentially only found in that Carpentries lesson. I edited to "curly brackets", which is the common name of braces in British English.
• The wording "standard QWERTY keyboard" is incorrect and also not inclusive. There is no standard QWERTY. I edited to clarify, although it's impossible to give a comprehensive instruction on where the | key is on all keyboard layouts.
• I edited an exercise adding a line to the solution rather than as a comment after the exercise.
• Typos in episode 1, fixes #329

[martinosorb]

The "software" part was meant to say that programs also have command line interfaces, rather than being "apps" with a GUI and that kind of stuff. How about "commands" or "programs"?

[tobyhodges]

Oh ok, I think I understand better now - I think this was a misunderstanding on my part, rather than something that needs to be improved in your wording.

Thanks for resolving the conflicts - I am going to merge the PR now.

[martinosorb]

Thank you!