Add Jan's examples to docs

[erikrose]

Once we get the docs branch landed—or maybe even before—we can add some of these examples care of Jan Moehrke. And give him credit!

• https://stackoverflow.com/questions/47982949/how-to-parse-complex-text-files-using-python/47984221#47984221
• https://stackoverflow.com/questions/63869794/parse-only-selected-records-from-empty-line-separated-file/63870354#63870354
• https://stackoverflow.com/questions/56011353/parsing-parameters-for-a-potential-function-using-parsimonious/56011540#56011540
• https://stackoverflow.com/questions/62597638/pandas-to-parse-the-text-data-and-aligned-the-columns-based-on-condition/62618506#62618506
• https://stackoverflow.com/questions/57067813/extract-text-enclosed-in-square-brackets-with-delimiter-between-properties-with/57070116#57070116