docs: add coupling to the --report-skip section list - #778

I went to drop the coupling section out of scc --report and the table in the README says you cant - every other section is in that list, coupling isn't. It works fine though, the table is just short a name. Passing a bogus section prints the real set:

$ scc --report=/tmp/r.html --report-skip bogus .
warning: --report-skip: unknown section "bogus" (recognised: cocomo, locomo, hotspots, coupling, authors, timeline, files, uloc, linelength, card)

The rest of the README has it right - the -h paste further up lists all ten, and the sentence directly under the table names coupling as one of the git-history sections. So it's only the table thats out of step. I've added it after hotspots, which is where the help puts it.

The same nine names in the same order also turn up in TestParseReportSkipKnownNames, under a comment saying it parses every recognised one. TestReportSkipRecognisedListMatchesSpec further down does have all ten and locks the size, so the set itself can't drift. Left that alone, it's a test rather than a doc.

I explicitly licence this contribution under the MIT licence.