Add TXTDirect's gometa article

[erbesharat]

Add an article about how to setup and monitor Go packages using TXTDirect and Prometheus.

Notes:
Not sure what else we need to cover to make the article more suitable for general readers who are not familiar with TXTDirect. Any suggestions?
Also, any ideas for the ending? Wasn't sure how we should end the article and what additional resources we should mention.

[ghost]

DeepCode Report (#15d27e)

DeepCode analyzed this pull request.
There are no new issues.

[stp-ip]

Why the specific choice to explain both vanity imports and metrics?
Would it be easier for the user to understand one at a time.
Aka Go imports via TXTDirect with just a domain and DNS TXT record and use TXTDirect to monitor incoming requests for things such as go imports etc. (could link to the first one)

[stp-ip]

The conclusion could probably point to txtdirect.com or a small example on how to set up gometa without hosting TXTDirect yourself and using our txtd.io endpoint instead.

[stp-ip]

Overall good. A few things. Still think a split from metrics and gometa might make sense.
And a few things might be able to be rephrased, can add a few more comments inline, if you want.

[stp-ip]

Let's rebase on latest master. Will do an inline review afterwards. Happy to get more posts out :)