Move docs to docs folder, rename files

docs/extensions/README.md

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+# Extensions
+
+Extensions go in the `./extensions/` folder, where exactly depends on which type of extension.
+
+- Extensions for checking status ("checkers") go in `./extensions/checkers/`
+- Extensions for alerting go in `./extensions/alerts/`
+- Extensions for logging go in `./extensions/logging/`
+
+Note that the folder name *must* be the same as the file name for the extension (excluding .py)!
+
+## Example
+
+```txt
+.
+├── extensions
+│   ├── alerts
+│   │   └── alerts_template
+│   │       └── alerts_template.py
+│   ├── checkers
+│   │   └── checker_template
+│   │       └── checker_template.py
+│   └── logging
+│       └── logging_template
+│           └── logging_template.py
+```
+
+## List of extensions
+
+There are none yet, so consider this secret a placeholder
+
+### Checkers
+
+### Alerts
+
+## Logging

docs/extensions/checkers.md

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+# Uptime Checker Extensions
+
+Updog doesn't do any monitoring by itself. Instead, extensions are used to check the status of whatever thing, send alerts, and log stuff. Updog just chains them together.
+
+Example extension: [askiiart/updog-checker_template](https://git.askiiart.net/askiiart/updog-checker_template)
+
+## Folder layout
+
+Extensions need to be put in the `./extensions/checkers` folder, and the name of the file must match the name of the folder.
+
+```txt
+.
+├── extensions
+│   ├── alerts
+│       └── alerts_template
+│           └── alerts_template.py
+```
+
+## Methods
+
+`*`: indicates a method is required
+
+### `__init__()`*
+
+**Arguments**:
+
+- A dict of arguments from `checker-args` in `services.json` - For no arguments, an empty dict will be used
+
+Example:
+
+```py
+{
+    "url": "https://example.net",
+    "port": 443
+}
+```
+
+**Return**: None
+
+### `get_status()`*
+
+**Arguments**: None
+
+**Return**: An integer indicating status; the codes; what the code means is provided by [`get_return_codes()`](#get_return_codes)
+
+These values can be overriden by providing [`get_return_codes()`](#get_return_codes)
+
+### `get_return_codes()`*
+
+**Arguments**: None
+
+**Return**: A `dict` containing integers and their associated statuses.
+
+Example:
+
+```py
+{
+    0: "Down",
+    50: "Partial outage",
+    100: "Up"
+}
+```