Revert "Revert "Readme for new wikis""

This reverts commit 43a9bf705d.

cfg/wiki_readme.txt

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+Hello! This is your new wiki directory. It contains various files that control
+how wiki looks and works. Here's a brief breakdown of them.
+
+wiki.git/
+    This is a Git repository that holds all of your wiki's content. If you want
+    to manually change something, add or remove files, do it there. Everything
+    inside is publicly accessible, so don't place something private in there.
+
+static/
+    This directory can be used to serve additional static files, or to overwrite
+    built-in ones. Here are some of the files you might want to place here:
+        common.css:     replaces Mycorrhiza Wiki's default stylesheet
+        custom.css:     adds additional styles to common.css
+        favicon.ico:    sets the website favicon
+
+cache/
+    This directory contains temporary files such as user tokens. You can
+    safely delete this directory, and nothing will break.
+
+README.txt
+    We're here! Feel free to remove this file if you don't need it.
+
+config.ini
+    This is the main configuration file that holds all your wiki's settings,
+    such as it's name, special hyphae, network configuration and, optionally,
+    additional JavaScripts.
+
+fixed-users.json
+    This file holds all fixed users' credentials. Not recommended to use.
+    See https://mycorrhiza.wiki/hypha/feature/authorization/fixed.
+
+registered-users.json
+    This file holds all registered users' credentials, securely hashed and
+    protected. This file is updated automatically, and you're discouraged from
+    editing it by yourself. More user control features are coming in the future.