Consistent cron argument lines in help detail and README.md

[magnetikonline]

Noted in the plugin things were a little inconsistent with regards to:

* * * * * %CUSTOM_ARG=value;ANOTHER=foo
* * * * * % CUSTOM_ARG=value; ANOTHER=foo

So moved everything in plugin/README.md to (less spaces):

* * * * * %CUSTOM_ARG=value;ANOTHER=foo

Also made some minor formatting tweaks to README.md (more things in inline code blocks and some whitespace/lines for readability).

[magnetikonline]

Also just noted that example in README.md was missing a final * in cron line - fixed in f448339.

[res0nance]

@magnetikonline I've kinda broken this PR, are you still interested in this?

[magnetikonline]

@res0nance ready to go - manually reapplied all edits against the current master.

[magnetikonline]

Thanks @res0nance 👍