Net tech docs

[jonathanglassman]

What problem does the pull request solve?

Implementing the Notify .NET client tech docs. I still have some questions that need answering as part of the review process:

1. In the "Add the Bintray package source (optional)" section, is the code specific to a particular CI tool?

2. In the "Set Mac OS environment variables" section, Mac OS has three fewer environment variables than Windows:

   • SETX SMS_SENDER_ID "valid sms_sender_id - to test sending to a receiving number, so needs to be a real number"
   • SETX API_SENDING_KEY "API_whitelist_key for sending an SMS to a receiving number"
   • SETX INBOUND_SMS_QUERY_KEY "API_test_key to get received text messages Is this correct?

Checklist

• [x] I’ve used the pull request template
• [ ] I’ve written unit tests for these changes
• [x] I’ve update the documentation (in README.md, CHANGELOG.md and CONTRIBUTING.md)
• [ ] I’ve bumped the version number (in src/Notify/Notify.csproj)

[servingUpAces]

The installation instructions for this client are extremely long. I'm not a .Net dev, but isn't some of this information common knowledge to dependency management? It would be great if we could shorten this section or move some information to another section like "more help with installation" which is not at the top of the docs.