Add a changelog

Adds an empty changelog file and a reminder to update it when opening
pull requests.

Also, adds a 1.0.0 version number in the package.json, which is what
we _could_ use for version numbering.

node_modules/.package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "codeql",
-  "version": "0.0.0",
+  "version": "1.0.0",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {