docs: bring README up to date

docs/README.md

@@ -1,6 +1,77 @@
-Docs
-====
+# Docs
 
-See the content directory for the docs in markdown format.
+This directory tree is uses to build all the different docs for
+rclone.
+
+See the `content` directory for the docs in markdown format.
+
+Note that some of the docs are auto generated - these should have a DO
+NOT EDIT marker near the top.
 
 Use [hugo](https://github.com/spf13/hugo) to build the website.
+
+## Changing the layout
+
+If you want to change the layout then the main files to edit are
+
+- `layout/index.html` for the front page
+- `chrome/*.html` for the HTML fragments
+- `_default/single.md` for the default template
+- `page/single.md` for the page template
+
+Running `make serve` in a terminal give a live preview of the website
+so it is easy to tweak stuff.
+
+## What are all these files
+
+```
+├── config.json                   - hugo config file
+├── content                       - docs and backend docs
+│   ├── _index.md                 - the front page of rclone.org
+│   ├── commands                  - auto generated command docs - DO NOT EDIT
+├── i18n
+│   └── en.toml                   - hugo multilingual config
+├── layouts                       - how the markdown gets converted into HTML
+│   ├── 404.html                  - 404 page
+│   ├── chrome                    - contains parts of the HTML page included elsewhere
+│   │   ├── footer.copyright.html - copyright footer
+│   │   ├── footer.html           - footer including scripts
+│   │   ├── header.html           - the whole html header
+│   │   ├── header.includes.html  - header includes eg css files
+│   │   ├── menu.html             - left hand side menu
+│   │   ├── meta.html             - meta tags for the header
+│   │   └── navbar.html           - top navigation bar
+│   ├── _default
+│   │   └── single.html           - the default HTML page render
+│   ├── index.html                - the index page of the whole site
+│   ├── page
+│   │   └── single.html           - the render of all "page" type markdown
+│   ├── partials                  - bits of HTML to include elsewhere
+│   │   └── version.html          - the current version number
+│   ├── rss.xml                   - template for the RSS output
+│   ├── section                   - rendering for sections
+│   │   └── commands.html         - rendering for /commands/index.html
+│   ├── shortcodes                - shortcodes for inserting bits of HTML
+│   │   ├── cdownload.html        - download the "current" version
+│   │   ├── download.html         - download a version with the partials/version.html number
+│   │   ├── provider.html         - used to make provider list on the front page
+│   │   └── version.html          - used to insert the current version number
+│   └── sitemap.xml               - sitemap template
+├── public                        - render of the website
+├── README.md                     - this file
+├── resources                     - don't know!
+│   └── _gen
+│       ├── assets
+│       └── images
+└── static                        - static content for the website
+    ├── css
+    │   ├── bootstrap.css
+    │   ├── custom.css            - custom css goes here
+    │   └── font-awesome.css
+    ├── img                       - images used
+    ├── js
+    │   ├── bootstrap.js
+    │   ├── custom.js             - custom javascript goes here
+    │   └── jquery.js
+    └── webfonts
+```