[aakashbansalgit]

Addresses #2070. The price adjustment page says what auto_adjust does but not how the dividend adjustment is calculated, which is behind several questions about returns not matching other sources. This adds three short sections to doc/source/advanced/price_adjustment.rst:

• How the dividend adjustment is calculated: the per-ex-date factor, 1 - dividend / previous close, and a snippet that rebuilds Adj Close from auto_adjust=False data.
• Adjusted prices change over time: each new dividend rescales all earlier prices, so stored adjusted prices drift from fresh downloads, and appending new adjusted rows to old ones creates a false jump.
• Adjusted close and total return: returns from adjusted prices are the same as reinvesting at the previous close minus the dividend, which is why they differ slightly from published total returns.

I checked the numbers before writing them down. The snippet matches Yahoo's Adj Close to within 0.004% over the full histories of KO, SPY, AGG and AAPL (KO goes back to 1962). The basis-point gaps in the last section are from January 2023 to September 2026 data.

Docs only, no code changes. Based on main because that is where the page is (#2992).