Fix copywriting nitpicks (Modules 5-8)

[ianjmacintosh]

Just like #386 here comes another PR to make the instructions a little clearer. Most of these edits are just little fiddly typo fixes, but I did a little bit of rephrasing and clarifying on the last 3 listed here.

• 1d595f1bc3eaf7e7dfc0325840d885d6ac1b2922: "Note: we're..." -> "Note: We're..."
• 7b1d195857a648ddd7accd5b95e2c62833e2684c: "Your's truly" -> "Yours truly"
• 0a07c9d5ab3f3dd735e6460e55468fded0c1317d: "react" -> "React"
• 9886d6b07ebb542779f04438f2a82db36afcec88: "sizelss" -> "sizeless"
• 4abd92874ddd00d5ce9e035b993b5da62ebedec6: Letting the student know the input name the integration test needs
• 9d0268e412726f434891fdb2a9c671c51916b3ce: This started as a typo fix, but then I reworded for clarity
• 5b5e53a9ffb5432731145fff1d4f8cad2b6df838: The checkbox lesson references checked but not its gotcha