More clearly specify when arguments can be passed multiple times

[panozzaj]

Hi, thanks for making this library, it was useful to me for inspecting a GraphQL endpoint.

I wanted to share that I had a little trouble getting it working since it wasn't totally clear how to pass multiple arguments of the same type (in my case -x for headers). I only thought to do this after seeing another library that said:

--header, -h    Add a custom header (ex. 'X-API-KEY=ABC123'), can be used multiple times

and digging into the code and seeing that it was part of a ListValueFlag. So then I tried multiple instances of -x and that seemed to work. I just kind of guessed at the format being "headername: header value".

Perhaps there is a way to make multiple parameters clearer in the documentation l like the get-graphql-schema library does? Or providing an example with multiple arguments.

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Also, the error I got before providing the correct arguments was unclear:

/Users/anthony/.nvm/versions/node/v18.19.1/lib/node_modules/@2fd/graphdoc/lib/schema-loader/http.js:53
                        return resolve(body.data.__schema);
                                                 ^

TypeError: Cannot read properties of undefined (reading '__schema')
    at Request._callback (/Users/anthony/.nvm/versions/node/v18.19.1/lib/node_modules/@2fd/graphdoc/lib/schema-loader/http.js:53:50)
    at self.callback (/Users/anthony/.nvm/versions/node/v18.19.1/lib/node_modules/@2fd/graphdoc/node_modules/request/request.js:185:22)
    at Request.emit (node:events:517:28)
    at Request.<anonymous> (/Users/anthony/.nvm/versions/node/v18.19.1/lib/node_modules/@2fd/graphdoc/node_modules/request/request.js:1154:10)
    at Request.emit (node:events:517:28)
    at IncomingMessage.<anonymous> (/Users/anthony/.nvm/versions/node/v18.19.1/lib/node_modules/@2fd/graphdoc/node_modules/request/request.js:1076:12)
    at Object.onceWrapper (node:events:631:28)
    at IncomingMessage.emit (node:events:529:35)
    at endReadableNT (node:internal/streams/readable:1400:12)
    at process.processTicksAndRejections (node:internal/process/task_queues:82:21)

It might have been better to say that no results were returned or there was an authentication error or something.

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Version: graphdoc v2.4.0