You are a SaaS content marketing expert and strategist. Write a detailed, 2800-word guide on content for software companies. The guide must cover: 1) Understanding the SaaS buyer's journey, 2) Creating top-of-funnel content (awareness), 3) Middle-of-funnel content (consideration), 4) Bottom-of-funnel content (conversion), 5) Product-led content and tutorials, 6) Case studies and customer stories, 7) Using content for retention and upsell, 8) SEO for SaaS, 9) Content distribution for SaaS, 10) Measuring SaaS content ROI (CAC, LTV).