move performance testing doc

Author: shakeelmohamed

contributor_docs/performance_testing.md

@@ -0,0 +1,18 @@
+<!-- Guide to writing performance tests for p5.js source code.  -->
+
+# Performance Testing
+
+Performance testing is an essential part of measuring how fasst isolated code paths take to execute under a known range of conditions.
+
+Implementation notes:
+
+- All pre-existing benchmarks included the full p5 instance setup which adds ~50ms to each test. The typography performance tests show how to isolate performance testing away from setup overhead.
+- The `textToPoints() single word, with render` test draws the calculated points, others just run `textToPoints()`.
+
+## Typography Tests
+
+To isolate typography tests, run the following:
+
+```shell
+npx vitest bench test/bench/typography.bench.js --reporter=verbose
+```