Change only section in README to new settings.

Use of these settings to follow.

README.md

@@ -132,30 +132,43 @@ module.exports = {
 After adding the config file, only implementations in `localConfig.cjs` will run.
 To only run specific implementations from the local config file see the [Using only](#using-only) section below.
 
-### Using only
-Local Implementations marked `only` will be the only implementations used in a test run.
-For example, to only run a single implementation in a suite set `only: true` in
-the local implementation manifest.
+### Test Suite Settings
+
+Additional test suite runtime configuration can be done via the `settings` key
+in a `localConfig.cjs`. The current global settings are:
+
+  * `disableInteropTests` - enable/disable the cross-implementation "interop" tests
+  * `testAllImplementers` - enable/disable testing _all_ implementations (not
+    just what's in `localConfig.cjs`)
+
+Both of these settings are `false` when `localConfig.cjs` is present, but may be
+overridden as below:
 
 ```js
-module.exports = [{
-  "name": "My Company",
-  "implementation": "My Implementation Name",
-  // this will ensure only this implementation is used in a suite
-  "only": true,
-  "issuers": [{
-    "id": "urn:uuid:my:implementation:issuer:id",
-    "endpoint": "https://localhost:40443/issuers/foo/credentials/issue",
-    "tags": ["eddsa-rdfc-2022"]
-  }],
-  "verifiers": [{
-    "id": "https://localhost:40443/verifiers/z19uokPn3b1Z4XDbQSHo7VhFR",
-    "endpoint": "https://localhost:40443/verifiers/z19uokPn3b1Z4XDbQSHo7VhFR/credentials/verify",
-    "tags": ["eddsa-rdfc-2022"]
-  }]
-}, {
-  ... some other implementation
-}];
+module.exports = {
+  "settings": {
+    // overriding the default, false, for local testing
+    "disableInteropTests": true,
+    "testAllImplementers": true
+  },
+  "implementations": [{
+    "name": "My Company",
+    "implementation": "My Implementation Name",
+    // this will ensure only this implementation is used in a suite
+    "only": true,
+    "issuers": [{
+      "id": "urn:uuid:my:implementation:issuer:id",
+      "endpoint": "https://localhost:40443/issuers/foo/credentials/issue",
+      "tags": ["eddsa-rdfc-2022"]
+    }],
+    "verifiers": [{
+      "id": "https://localhost:40443/verifiers/z19uokPn3b1Z4XDbQSHo7VhFR",
+      "endpoint": "https://localhost:40443/verifiers/z19uokPn3b1Z4XDbQSHo7VhFR/credentials/verify",
+      "tags": ["eddsa-rdfc-2022"]
+    }]
+  }, {
+    // Add additional implementations as needed
+  }];
 ```
 
 ### Tags