[Epic 8.3] Update README with new builder API examples

[ooples]

User Story

As a potential user, I want the README to showcase the new builder API so that I can see how to use the library.

Acceptance Criteria

• README.md updated with v2.0 examples
• Quick start section with builder pattern
• Performance badges/claims with benchmark links
• Comparison with other libraries
• Links to full documentation

README Sections

1. Installation

   dotnet add package OoplesFinance.StockIndicators
   

2. Quick Start

   var builder = new StockIndicatorBuilder(source)
       .ConfigureIndicators(i => {
           var sma = i.Sma(20);
           var rsi = i.Rsi(14);
       })
       .ConfigureSignals(s => {
           s.When(rsi).CrossesAbove(70).Emit("overbought");
       });

3. Performance

   • Zero heap allocations
   • SIMD-accelerated calculations
   • Benchmark results

4. Features

   • 750+ indicators
   • Streaming support
   • Notification adapters
   • Auto-trading integration

Dependencies

• All implementation epics complete