Document in README and add schema test.

.github/workflows/verify-schema.yaml

@@ -0,0 +1,11 @@
+on: push
+name: Check that the JSON schema for the configuration file matches the examples
+jobs:
+  integration_tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v1
+      - name: Use Node.js
+        uses: actions/setup-node@v1
+      - run: npm install -g pajv
+      - run: make -C schema

README.md

@@ -151,6 +151,22 @@ ignore-gitignore: false
 max-file-size-kb: 100
 ```
 
+## Configuration file schema
+
+There is a JSON Schema definition for the `static-analysis.datadog.yml` in the `schema` subdirectory.
+
+You can use it to check the syntax of your configuration file:
+
+1. Install https://www.npmjs.com/package/pajv (`npm install -g pajv`)
+2. Execute `pajv validate -s schema/schema.json -d path/to/your/static-analysis.datadog.yml`
+
+There are some examples of valid and invalid configuration files in the [`schema/examples/valid`](schema/examples/valid)
+and [`schema/examples/invalid`](schema/examples/invalid) subdirectories, respectively. If you make changes to the JSON
+Schema, you can test them against our examples:
+
+1. Install https://www.npmjs.com/package/pajv (`npm install -g pajv`)
+2. Execute `make -C schema`
+
 ## Other Tools
 
 ### datadog-export-rulesets