Reads inst/app/about.md and fills in how often the data are
downloaded again, so that the text follows history_minutes.
Examples
cat(substr(golemstockindices:::about_text(), 1, 300))
#> Stock Market Indices shows the daily prices of the major stock market indices of the Americas, Europe and Asia-Pacific, from <a href="https://finance.yahoo.com" target="_blank" rel="noopener">Yahoo Finance</a>. This page explains what each index measures, what each tab shows and how its numbers are