Add readme how to use the script

xrpl-hooks-docs/README.md

@@ -0,0 +1,15 @@
+# How to generate markdown from language server rst-files
+
+Go to xrpl-hooks-docs folder
+`cd xrpl-hooks-docs`
+
+Then run the `convert-to-md.js` script in that folder:
+`node convert-to-md.js`
+
+If everything goes well this should output `xrpl-hooks-docs-files.json` file which contains array of the error codes and markdown related to that.
+
+Something like this:
+
+```json
+{"code":"hooks-account-buf-len","markdown":"hooks-account-buf-len\n---\n\nFunction `hook_account` has fixed-size account ID output.\n\nThis check warns about too-small size of its output buffer (if it's\nspecified by a constant - variable parameter is ignored).\n\n"},{"code":"hooks-account-conv-buf-len","markdown":"hooks-account-conv-buf-len\n---\n\nFunction `util_raddr` has fixed-size account ID input.\n\nThis check warns unless the correct size is passed in the input size\nparameter (if it's specified by a constant - variable parameter is\nignored).\n"}]
+```