If I were doing this in the shell, the syntax would look something like..
"C:\Users\myuser\AppData\Local\Google\Chrome\Application\chrome.exe" "file:///C:/Users/myuser/Desktop/index.html#anchor1"
here's one, admittedly crude, way to do that in IA:
1) employ a small jar program that finds browsers (stackoverflow)
2) then your program will compose a couple of strings and write them to a .bat or .sh file - ie the command(s) string to open the browser and the string for your local readme
3) then your program can either pass the "special folder" back to IA using custom code, or, for expediency, execute it directly if you don't care how it happens.
4) this produces a browser scrolled down to the right anchor.
the alternative actions of "open default browser", or "launch file", provided by IA api seems to strip (or not allow) the #anchor annotation in url's.