Add comments to examples to make them more obvious

[esnible]

For #241

First step at adding more comments to document examples.

[vazirim]

@esnible I believe you still need -f ./multi-prompts.json?

[esnible]

Try it yourself? I did pdl multi_round_chat.pdl and from the home directory pdl examples/granite/multi_round_chat.pdl. Both worked.

[vazirim]

You are right, we have an include so -f is not needed. Leftover from old ways of doing things.

[starpit]

btw, as far as i can tell, source comments do not propagate to the trace json. whereas inline text elements to. could we leverage those more, instead of source comments?

[esnible]

@starpit I agree that I would like to see comments when debugging.

• PDL uses PyYAML, which doesn't see them. An alternative is to switch to https://pypi.org/project/ruamel.yaml/ . Not sure of the difficulty. That parser preserves ordering and comments.
• Somehow PDL knows the line number of statements. An alternative is to include the PDL source in the trace, then use the line number to navigate to the original representation.
• It might be possible to add a comment field to PDL's basic block. However, that looks ugly and couldn't handle blocks such as - "\nDid you say ${ GEN }?\n" # Did the user say $GEN?

[vazirim]

PDL has a description field in every block which is basically a comment.

For a string by itself you can write:

- text: "\nDid you say ${ GEN }?\n" 
  description: "Did the user say $GEN?"

[starpit]

fib.pdl uses plain text elements that show up nicely (well, it could be nicer, work in progress) as notebook-style interstitial commentary.