added diagnostic notes

Diag.md

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+# Diagnostics
+
+## Get human version
+```js
+console.log(human.version);
+```
+```
+2.2.0
+```
+
+## Enable console debug output
+```js
+const human = new Human({ debug: true })
+```
+
+## Get current configuration
+```js
+console.log(human.config)
+```
+```js
+{
+  backend: 'tensorflow',
+  modelBasePath: 'file://models/',
+  wasmPath: 'https://cdn.jsdelivr.net/npm/@tensorflow/tfjs-backend-wasm@3.9.0/dist/',
+  debug: true,
+  ...
+}
+```
+
+## Get current environment details
+```js
+console.log(human.env)
+```
+```json
+{
+  "browser": true,
+  "node": false,
+  "worker": false,
+  "platform": "Windows NT 10.0; Win64; x64",
+  "agent": "Mozilla/5.0 AppleWebKit/537.36 Chrome/95.0.4629.0 Safari/537.36 Edg/95.0.1011.0",
+  "backends": ["cpu","webgl","wasm"],
+  "tfjs": {"version":"3.9.0"},
+  "wasm": {"supported":true,"simd":true,"multithread":true},
+  "webgl": {"supported":true,"version":"WebGL 2.0 (OpenGL ES 3.0 Chromium)","renderer":"WebKit WebGL"},
+  "webgpu": {"supported":true,"adapter":"Default"},
+  "kernels": [...]
+}
+```
+
+## Get list of all models
+```js
+  const models = Object.keys(human.models).map((model) => ({ name: model, loaded: (human.models[model] !== null) }));
+  console.log(models);
+```
+```js
+[
+  { name: 'face', loaded: true },
+  { name: 'posenet', loaded: false },
+  { name: 'blazepose', loaded: false },
+  { name: 'efficientpose', loaded: false },
+  { name: 'movenet', loaded: true },
+  { name: 'handpose', loaded: true },
+  { name: 'age', loaded: false },
+  { name: 'gender', loaded: false },
+  { name: 'emotion', loaded: true },
+  { name: 'embedding', loaded: false },
+  { name: 'nanodet', loaded: false },
+  { name: 'centernet', loaded: false },
+  { name: 'faceres', loaded: true },
+  { name: 'segmentation', loaded: false },
+]
+```
+
+## Get memory usage information
+```js
+  console.log(human.tf.engine().memory()));
+```
+
+```js
+{
+  numTensors: 1053, numDataBuffers: 1053, numBytes: 42736024
+}
+```
+
+## Get current TensorFlow flags
+```js
+  console.log(human.tf.ENV.flags);
+```
+```js
+{
+  IS_BROWSER: false, IS_NODE: true, DEBUG: false, CPU_HANDOFF_SIZE_THRESHOLD: 128, PROD: true
+}
+```
+
+## Get performance information
+
+```js
+  const result = await human.detect(input);
+  console.log(result.performance);
+```
+```js
+  {
+    backend: 1, load: 283, image: 1, frames: 1, cached: 0, changed: 1, total: 947, draw: 0,
+    face: 390, emotion: 15, embedding: 97, body: 97, hand: 142, object: 312, gesture: 0
+  }
+```