Add md files for auto index pages

Part of IA and Redocly migration work. Create simple .md files to
represent the automatic index pages that previously only existed in
the dactyl-config.yml file. (The code used to do this is also part
of the commit but is, hopefully, no longer needed.)

content/references/http-websocket-apis/public-api-methods/transaction-methods/index.md

@@ -0,0 +1,7 @@
+---
+html: transaction-methods.html         # watch for clashes w/ this filename
+parent: public-api-methods.html
+template: pagetype-category.html.jinja
+---
+# Transaction Methods
+Transactions are the only thing that can modify the shared state of the XRP Ledger. All business on the XRP Ledger takes the form of transactions. Use these methods to work with transactions.