pkg/p256k1/docs

• BENCHMARK_REPORT_AVX2.md
• BENCHMARK_RESULTS.md
• GLV_STRAUSS_WNAF.md
• IMPLEMENTATION_PLAN_GLV_WNAF.md
• MONTGOMERY_NOTES.md
• README_p256k1.md
• memory-optimization-results.md
• why_secp256k1.md