Update section headers to use the active voice

[fredjaya]

Currently, a lot of Part 1 headers (and subheaders) mention a thing, but these can be improved to be more informative and provide context on the thing that will actually be done by attendees.

Some examples:

• Task directories -> Find the output and logs in the task directories

• Output -> Defining the output block in your process

• Channel.of() -> Providing inputs using Channel.of()

• Review for Part 2 sections too

• Add indexes to headers e.g. 1.0.1 Title, 1.1.2 Title 2