More understandable error message when max_document_size has been reached

## Expected Behavior
Understandable error message

## Current Behavior
I was getting this error suddenly on every insert operation:

Error: users at responseHandler (../node_modules/nano/lib/nano.js:193:20) at ../node_modules/nano/lib/nano.js:442:13 at process.processTicksAndRejections (node:internal/process/task_queues:95:5)

## Possible Solution
I updated the max_document_size in the couchdb configs

## Context
I spent 3 days trying to find out what this error meant. Maybe it would be useful for developers if the error message was a bit more understandable.

Reproduce an insert after reaching CouchDB's max_document_size, then inspect the response handling shown at ../node_modules/nano/lib/nano.js:193 and 442. Trace the server response that currently becomes only “Error: users” and identify the expected clearer message; done means the size-limit failure is understandable to developers.

Written by the indexing model from the issue text.