Explain NIMFLAGS="-d:insecure" for nimbus

[eccentricexit]

Really like the dashboard so far, however I am reluctant to build nimbus with that flag as instructed without knowing what it does.
The current nimbus book also does not explain what that flag does.

What does it do? Is actually insecure?

eth2-grafana/nimbus/README.md

Line 19 in 3d119f5

1. Build Nimbus using `NIMFLAGS="-d:insecure"` command-line parameter, following the [Grafana and Prometheus](https://nimbus.guide/metrics-pretty-pictures.html) section of [The Nimbus Book](https://nimbus.guide/)

[metanull-operator]

I will look into it. I do not see that flag referenced on the Nimbus page any longer, so this may no longer be necessary. Thanks for the notice.