docs: document setting column widths via configureOptionsUsing (#213)

[elminson]

Why

#213 ("Auto size Excel column width") has been open since 2021 with 7 comments, and the answer on the thread is that widths are not possible. That is only half true: explicit column widths already work through OpenSpout's writer options and configureOptionsUsing() — it was simply never documented. Several commenters were asking for exactly this.

Change

Docs only, no code. Adds an "Set column widths" section under Advanced usage covering:

• setColumnWidth(width, ...$columns) and setColumnWidthForRange(width, $start, $end)
• that column numbers are 1-based
• that it works with streaming exports (cursor/generator), because widths are written when the file is finalized rather than per row
• that xlsx/ods support widths and csv ignores them
• an explicit note that automatic sizing to fit content is still unavailable

Verified

Every snippet was run before being documented:

Snippet	Result
setColumnWidth(40, 1) + setColumnWidth(15, 2, 3)	<col min="1" max="1" width="40"/><col min="2" max="3" width="15"/>
setColumnWidthForRange(20, 1, 4)	<col min="1" max="4" width="20"/>
same, from a generator (streaming)	<col min="1" max="1" width="33"/>
ods export	writes successfully

Refs #213 — deliberately not "Closes", since auto-sizing is the actual request and remains open.

[elminson]

Hi @dannyyol 👋 — gentle nudge that this is waiting on your review.

It is docs-only, no code: it documents that explicit column widths already work through configureOptionsUsing() + setColumnWidth(), which is the part of #213 that is solvable today. Every snippet in it was run before being written down. Should be a quick read.

Thanks, and enjoy your weekend! 🙌