Better describe the Interscript Conversion Language on interscript.org

[ronaldtse]

@webdev778 can you help describe the language on interscript.org? Thanks.

Originally posted by @ronaldtse in interscript/interscript-ruby#718 (comment)

[ronaldtse]

We already have it: https://www.interscript.org/develop/Interscript_Map_Format but perhaps it's a content issue we need to describe more in depth.

https://www.interscript.org/develop/Map_Editing_Guide as well