Add .gitignore and improve documentation with profiling notes

Co-authored-by: T-Gro <46543583+T-Gro@users.noreply.github.com>

Author: Copilot

tools/perf-repro/.gitignore

@@ -0,0 +1,17 @@
+# Generated test projects
+generated/
+
+# Profiling results
+results/
+
+# Trace files
+*.nettrace
+*.speedscope.json
+
+# Build artifacts from generated projects
+**/bin/
+**/obj/
+
+# Temporary files
+*.log
+build.log

tools/perf-repro/PERF_REPORT.md

@@ -1,5 +1,7 @@
 # F# Compiler Performance Analysis - xUnit Assert.Equal Issue #18807
 
+*This is a sample/template report showing the expected output format*
+
 *Generated: 2025-11-11 13:21:15*
 
 ## Test Configuration

tools/perf-repro/README.md

@@ -133,7 +133,7 @@ dotnet fsi AnalyzeTrace.fsx --results ./results
   dotnet tool install -g dotnet-trace
   ```
 
-**Note:** The suite will work without `dotnet-trace` by falling back to timing-only mode.
+**Note:** The suite will work without `dotnet-trace` by falling back to timing-only mode. When trace collection is enabled, expect significant slowdown (3-10x) during profiling - this is normal and necessary to capture detailed execution data.
 
 ## Understanding the Results
 
@@ -199,6 +199,8 @@ The suite will work in timing-only mode. For detailed trace analysis, install:
 dotnet tool install -g dotnet-trace
 ```
 
+**Note**: Trace collection adds significant overhead (3-10x slowdown) to build times. This is normal and expected when profiling.
+
 ### Permission Errors on Linux/macOS
 
 Make scripts executable: