Mention a more performant JSON validator (#241)

It does users a disservice to direct them to `check-jsonschema` in the
first instance.

`check-jsonschema` is incredibly slow (probably because of Python
interpreter startup time) when run in a loop on multiple files.

---------

Signed-off-by: Andrew Pollock <andrewpollock@users.noreply.github.com>

validation/README.md

@@ -2,7 +2,13 @@
 
 This directory contains a JSON schema to validate OSV entries.
 
-## Usage
+## Example Usage
+
+(Any [validator](https://json-schema.org/implementations#validators) can be used, these are a couple that are known to work)
+
+```
+$ go run github.com/neilpa/yajsv@latest -s schema.json osv_to_test.json
+```
 
 ```
 $ pip install check-jsonschema