[rrd4j] improvements and extensions to documentation

[andrewfg]

When I tried to set up rrd4j persistence on my own system, I found the rrd4j ReadMe.md documentation in general very hard to understand, and in particular missing some specific information.

Very kindly @JueBag helped me to solve it -- thank you!

So, based on our common learning, this PR contains improvements and extensions to the ReadMe.md file (it also contains a small change in the .cfg sample file in which the parameter names have been changed to match the documentation).

[andrewfg]

@JueBag this fails the DCO because your commit sha: be0820a reported Expected "Jürgen Baginski opus42@gmx.de", but got "Jürgen Baginski opus42@gmx.de" -- I am not sure what that means, or how to fix it (???)

[JueBag]

Again a problem with the SignOff, I have no idea why and how to fix it. Sorry for that.

[andrewfg]

@9037568 I have pushed your proposed changes. Do you know why the DCO test keeps failing?

[9037568]

I haven't the first clue about the DCO. The values it's claiming don't match look like they match to me. Thanks for the changes.

[andrewfg]

@9037568 in the meantime, it seems that all tests have passed. I don’t know why it errored before, but anyway it is “all green now”.

[openhab-bot]

This pull request has been mentioned on openHAB Community. There might be relevant details there:

https://community.openhab.org/t/maximumsince-isnt-the-maximum/99249/22

[andrewfg]

Ping!

IMHO this PR is ready to be published. Note: it is documentation only..

[kaikreuzer]

@andrewfg May I ask you to create another PR to make the same update available in openHAB 3 at https://github.com/openhab/openhab-addons/tree/master/bundles/org.openhab.persistence.rrd4j? Thanks!

[andrewfg]

@andrewfg May I ask you to create another PR to make the same update available in openHAB 3 at https://github.com/openhab/openhab-addons/tree/master/bundles/org.openhab.persistence.rrd4j? Thanks!

@kaikreuzer ok, done.

[kaikreuzer]

Thanks!