Clarify and add more inline guidance wrt OSM tags

[tuukka]

In addition to the links to the OSM wiki pages about each form field, it might make it much easier to new users if each field and option included a short inline description. I think the goal should be that in most cases, a new user shouldn't need to consult the wiki pages.

E.g. "Type of use of this entrance
Exit only
Door to a home"
Normal (main) entrance for the public
Unspecified (none of the above)

Regarding the address fields, I think it's a great idea to include an example as a placeholder. In addition, you could include a complete example with the relevant part in bold, e.g. "Entrance reference (e.g. Kirkkokatu 24 B 13) example: B" Ideally, these would be localised based on the country information.