doc: add more context about benchmark tests and envs used

Author: brunocroh

doc/contributing/writing-and-running-benchmarks.md

@@ -707,3 +707,38 @@ Supported options keys are:
 [node-benchmark-compare]: https://github.com/targos/node-benchmark-compare
 [t-test]: https://en.wikipedia.org/wiki/Student%27s_t-test#Equal_or_unequal_sample_sizes%2C_unequal_variances_%28sX1_%3E_2sX2_or_sX2_%3E_2sX1%29
 [wrk]: https://github.com/wg/wrk
+
+### Creating Benchmark Tests
+
+It is recommended to create a new test file when a new benchmark is introduced
+so it can be easily made creating the new test file in `test/benchmark`.
+
+When calling the `runBenchmark`, provide the benchmark group name
+(which is the folder name in the `benchmark/` folder) as the first parameter,
+and optionally pass environment variables as the second parameter.
+
+```js
+'use strict';
+
+require('../common'); // Import the common module - required for all benchmark files
+
+const runBenchmark = require('../common/benchmark');
+
+runBenchmark('buffers', { NODEJS_BENCHMARK_ZERO_ALLOWED: 1 });
+```
+
+The environment variable `NODEJS_BENCHMARK_ZERO_ALLOWED` is necessary
+if the test runs so fast that it can result in errors or flaky tests.
+Setting this environment variable will make the benchmark ignore these issues.
+
+The way tests will be executed depends on the environment variable `NODE_RUN_ALL_BENCH_TESTS`.
+If it is set to **true**, benchmarks run with minimal iterations (`n=1`, `rounds=1`).
+The idea here is to ignore performance analysis and just check if it can run without failing.
+Despite running the minimal amount, it still consumes too much time to run
+because it needs to run all configurations.
+
+Otherwise, when `NODE_RUN_ALL_BENCH_TESTS` isn't set,
+only one configuration per benchmark is executed.
+This significantly reduces execution time but offers limited coverage
+and cannot ensure all configurations work correctly.
+