Add `prf:example` environment to Examples in the lectures

[longye-tian]

We want to add

```{prf:example}
:label: example_label

(We need to have labels if there are more than two examples and there is a space after the :, and there is no space for prf:example).

to examples to the intro lecture series.

• [ ] ak2.md (exist current PR #508, wait to avoid merge conflict)
• [x] ar1_processes.md (added in #538 )
• [x] business_cycle.md (checked by #538 , no need to add example admonition)
• [x] cagan_adaptive.md (checked by #538 , no need to add example admonition)
• [x] cagan_ree.md (checked by #538 , no need to add example admonition)
• [x] cobweb.md (checked by #538 , no need to add example admonition)
• [x] commod_price.md (checked by #538 , no need to add example admonition)
• [x] complex_and_trig.md (added in #538 )
• [x] cons_smooth.md (checked by #538 , no need to add example admonition)
• [x] eigen_I.md (add one example admonition by #538 )
• [x] eigen_II.md (add two example admonitions by #538 )
• [ ] equalizing_difference.md (exist current PR #522 , wait to avoid merge conflict)
• [ ] french_rev.md (exist current PR #525 , wait to avoid merge conflict)
• [ ] geom_series.md (exist current PR #524 , wait to avoid merge conflict)
• [ ] greek_square.md (exist current PR #525 , wait to avoid merge conflict)
• [x] heavy_tails.md (add two example admonitions by #538 )
• [x] inequality.md (add one example admonition by #538 )
• [ ] inflation_hisotry.md (exist current PR #525 , wait to avoid merge conflict)
• [x] input_output.md (add two example admonitions by #538 )
• [x] intro_supply_demand.md (add two example admonitions by #543 )
• [x] laffer_adaptive.md (checked by #545 , no need to add example admonition)
• [x] lake_model.md (checked by #545 , no need to add example admonition)
• [x] linear_equations.md (added by #528 )
• [x] lln_clt.md (added two examples by #536 )
• [x] long_run_growth.md (checked, no example to add)
• [x] lp_intro.md (checked by #531 )
• [ ] markov_chain_I.md (exist current PR #479 , wait to avoid merge conflict)
• [x] markov_chain_II.md (add three example admonitions by #546 )
• [x] mle.md (add one example admonitions by #546 )
• [x] money_inflation.md (checked by #546 , no need to add example admonition)
• [x] money_inflation_nonlinear.md (checked by #546 , no need to add example admonition)
• [ ] monte_carlo.md
• [ ] networks.md
• [ ] olg.md
• [ ] prob_dist.md
• [ ] pv.md
• [ ] scalar_dynam.md
• [ ] schelling.md
• [ ] short_path.md
• [ ] simple_linear_regression.md
• [ ] solow.md
• [ ] supply_demand_heterogeneity.md
• [ ] supply_demand_multiple_goods.md
• [ ] time_series_with_matrices.md (exist current PR #534 , wait to avoid merge conflict)
• [x] unpleasent.md (checked and no example added #535 )

[mmcky]

thanks @longye-tian this would be a great task. When making edits it would be helpful to edit in batches to reduce the possibility of merge conflicts.

[longye-tian]

thanks @longye-tian this would be a great task. When making edits it would be helpful to edit in batches to reduce the possibility of merge conflicts.

Hi Matt,

I definitely agree. I will first choose the lecture without any open pull request to work on.

Best, Longye