instrumenting: add Rust client library link.

Fix usage of anchored regex in federation example.

file_sd_config: Correct refresh_interval to 5m

The actual default is 5 minutes:
https://github.com/prometheus/prometheus/blob/ee9abf4535d2a28feb14473716e9118b4e12741b/config/config.go#L106

This was changed in prometheus/prometheus@139f27bf8.

Add template to redirect people to docs repo for changes

Hopefully this will help people to not create PRs against the generated
repo.

Added NATS exporter to list of 3rd party exporters

Lovoo (whose Jenkins exporter is listed) also have a NATS exporter which I have added

Point to better Jenkins exporter

The RP jenkins exporter is meant mainly as a simple example of an exporter. The Lovoo version builds on this.

Update kubernetes link to use the new github org

The old one redirects, but better to be up to date I think.

Revert "Added docs for toLower and toUpper formatting"

Added docs for toLower and toUpper formatting

Point users to Matrix/Vector bridge for IRC access

Update ruby support for histograms

Add Julius to commercial support section

At least for the moment...

Unit examples should be seconds

Blog post: "Pull does not scale - or does it?"

Add grok_exporter

Add some CNCF branding.

Clarify DNS service discovery relationship to DNS-SD

It's a common misconception to call any DNS SRV record based discovery
approach "DNS-SD". The latter is a [ratified IETF standard][rfc6763]
which specifies a naming schema and lookup mechanism in order to provide
additional structured information. Prometheus only supports basic SRV
record lookups.

[rfc6763]: https://tools.ietf.org/html/rfc6763

Emphasize the cumulative nature of a histogram.

Link the relevant Wikipedia entry.

Add reference to PHP client library