docs(models generation): adds readme

README.md

@@ -7,6 +7,83 @@ Model converters and codegen for [Concerto](https://github.com/accordproject/con
 npm install @accordproject/concerto-codegen --save
 ```
 
+## Use
+
+### Benchmark Model Generator
+
+This API allows you to generate models of varying sizes which can be used to test the performance of your Concerto-handling code.
+
+#### Generate a model up to a specified number of declarations and properties
+
+You can generate a model up to a specified number of declarations and properties using:
+
+```js
+const benchmarkModelGenerator = new BenchmarkModelGenerator();
+const generated = benchmarkModelGenerator.generateConcertoModels({
+    nDeclarations: 5, // Number of declarations in the model
+    nProperties: 5, // Number of properties per declaration
+});
+```
+
+#### Generate a model up to a specified size in bytes
+
+You can generate a model up to a specified size in bytes, however you would need to specify how that model should grow.
+
+##### Grow model by number of declarations
+
+If you'd like to grow it by number of declarations, you will need to specify the number of properties that you wish the model to have (defaults to `1`):
+
+```js
+const benchmarkModelGenerator = new BenchmarkModelGenerator();
+const generated = benchmarkModelGenerator.generateConcertoModels({
+    generateUpToSize: 10000, // Target upper limit of growth in bytes
+    growBy: 'declarations', // Element type by which the model should grow
+    nProperties: 5, // Number of properties per declaration
+});
+```
+
+##### Grow model by number of properties
+
+If you'd like to grow it by number of properties, you will need to specify the number of declarations that you wish the model to have (defaults to `1`):
+
+```js
+const benchmarkModelGenerator = new BenchmarkModelGenerator();
+const generated = benchmarkModelGenerator.generateConcertoModels({
+    generateUpToSize: 10000, // Target upper limit of growth in bytes
+    growBy: 'properties', // Element type by which the model should grow
+    nProperties: 5, // Number of declarations in the model
+});
+```
+
+The expected response will include an array of generated `models` (currently containing only a single model) and a `metadata` object with information about the generated model e.g:
+
+```js
+{
+  models: [
+    {
+      '$class': '[email protected]',
+      decorators: [],
+      namespace: '[email protected]',
+      imports: [],
+      declarations: [
+        ...
+      ]
+    }
+  ],
+  metadata: {
+    requestedModelSizeInBytes: 10000,
+    humanReadableRequestedModelSize: '9.77 KiB',
+    generatedModelSizeInBytes: 9952,
+    humanReadableGeneratedModelSize: '9.72 KiB',
+    declarationsN: 5,
+    propertiesNInSmallestDeclaration: 15,
+    propertiesNInLargestDeclaration: 16
+  }
+}
+```
+
+As you can see from the above example model, the generator will try its best to reach the upper `generateUpToSize` reqested size, but may fall short by a few bytes.
+
 ## License <a name="license"></a>
 Accord Project source code files are made available under the Apache License, Version 2.0 (Apache-2.0), located in the LICENSE file. Accord Project documentation files are made available under the Creative Commons Attribution 4.0 International License (CC-BY-4.0), available at http://creativecommons.org/licenses/by/4.0/.