docs(british-english): remove redundant guidance line
The "Follow these rules consistently throughout a document." line
added no real directive beyond what the rule sections already convey,
and the "a document" framing was too narrow for outputs like commit
messages and code comments.
@
Adds a British English writing-conventions skill covering -ise/-our/-re/-ence/-ogue spellings, doubled-l verb forms, programme vs program, punctuation (single quotes, logical punctuation, spaced en dashes, Oxford comma), vocabulary, dates/times, grammar (collective nouns, shall/will, prepositions, present perfect), measurements and currency. Polishes a few entries on second pass: doubled-l wording, mediaeval note, en-dash example, and 'informal' label.
siujamo
