#167 Fix grammar & typos: minor fixes across modeling guides

Summary

Fix small grammar, punctuation, and formatting issues in three modeling guides. No content or wording rewrites.

Changes

• guides/modeling/building-p-and-l.mdx
  • Lowercase mid-sentence "In" → "in" after Click \edit`andClick edit`.
  • Repair sentence fragment + malformed link: categories. Follow directions to create a[ Data source-powered lookup] → categories, follow directions to create a [Data source-powered lookup].
• guides/modeling/lookups.mdx
  • Add missing article: "will populate as column" → "will populate as a column".
• guides/modeling/revenue-recognition.mdx
  • Add missing spaces between inline code and bold: `is on or before`**This month** → `is on or before` **This month** (and the two adjacent lines).
  • Add missing apostrophe: "the drivers formulas" → "the driver's formulas".

---

Summary by cubic

Fixes small grammar and formatting issues across three modeling guides to improve readability. No content changes.

• Bug Fixes
  • guides/modeling/building-p-and-l.mdx: lowercased mid-sentence "In" after "Click edit"; fixed a fragment and malformed link; repeated lowercase fix later.
  • guides/modeling/lookups.mdx: added missing "a" in "populate as a column".
  • guides/modeling/revenue-recognition.mdx: added spaces between inline code and bold tokens; corrected the "driver's formulas" apostrophe.