Add language codes topic to search help

[rmglennon]

This adds a new file about language support to the published search help on mapzen.com.

cc @dianashk @missinglink

[rmglennon]

preview: https://precog.mapzen.com/mapzen/documentation/5a3fe3bfc9c3784afcfce651f5a10dd883a7d782/documentation/search/language-codes/

[missinglink]

looks good! we could optionally include some information about the geocoding (header part) of the response JSON.

eg:

{
  "geocoding": {
      ...
      "lang": {
        "name": "German",
        "iso6391": "de",
        "iso6393": "deu",
        "defaulted": false
      },
      ...
    },
...

we return information in this block about the language which the system decided to use, this is useful for users to debug responses.

the block should always be present and should always contain 4 keys:

• name: a human readable name for the language (in English) #owwowhowmeta
• iso6391/iso6393: the language code as defined in the two most common standards
• defaulted: true/false to idicate if we 'fell back' to using a default language property

[missinglink]

note that for the query above I used ?lang=de-ch which refers to Swiss German and the response was returned in 'High German' ie Deutsch.

[rmglennon]

thanks, @missinglink - I can add this content over in pelias-doc repository.