Added docs for introspection endpoints

https://datasette.readthedocs.io/en/latest/introspection.html

docs/config.rst

@@ -1,5 +1,7 @@
-Config
-======
+.. _config:
+
+Configuration
+=============
 
 Datasette provides a number of configuration options. These can be set using the ``--config name:value`` option to ``datasette serve``.
 

docs/index.rst

@@ -23,6 +23,7 @@ Contents
    full_text_search
    metadata
    config
+   introspection
    custom_templates
    plugins
    changelog

docs/introspection.rst

@@ -0,0 +1,113 @@
+Introspection
+=============
+
+Datasette includes some pages and JSON API endpoints for introspecting the current index. These can be used to understand some of the internals of Datasette and to see how a particular instance has been configured.
+
+Each of these pages can be viewed in your browser. Add ``.json`` to the URL to get back the contents as JSON.
+
+/-/metadata
+-----------
+
+Shows the contents of the ``metadata.json`` file that was passed to ``datasette serve``, if any. `Metadata example <https://fivethirtyeight.datasettes.com/-/metadata>`_::
+
+    {
+        "license": "CC Attribution 4.0 License",
+        "license_url": "http://creativecommons.org/licenses/by/4.0/",
+        "source": "fivethirtyeight/data on GitHub",
+        "source_url": "https://github.com/fivethirtyeight/data",
+        "title": "Five Thirty Eight",
+        "databases": {...}
+    }
+
+/-/inspect
+----------
+
+Shows the result of running ``datasette inspect`` on the currently loaded databases. This is run automatically when Datasette starts up, or can be run as a separate step and passed to ``datasette serve --inspect-file``.
+
+This is an internal implementation detail of Datasette and the format should not be considered stable - it is likely to change in undocumented ways between different releases.
+
+`Inspect example <https://fivethirtyeight.datasettes.com/-/inspect>`_::
+
+    {
+        "fivethirtyeight": {
+            "file": "fivethirtyeight.db",
+            "hash": "5de27e3eceb3f5ba817e0b2e066cea77832592b62d94690b5102a48f385b95fb",
+            "tables": {
+                "./index": {
+                    "columns": [
+                        "dataset_url",
+                        "article_url",
+                        "live"
+                    ],
+                    "count": 125,
+                    "foreign_keys": {
+                        "incoming": [],
+                        "outgoing": []
+                    },
+                    "fts_table": null,
+                    "hidden": false,
+                    "label_column": null,
+                    "name": "./index",
+                    "primary_keys": []
+                },
+                ...
+
+
+/-/versions
+-----------
+
+Shows the version of Datasette, Python and SQLite. `Versions example <https://fivethirtyeight.datasettes.com/-/versions>`_::
+
+    {
+        "datasette": {
+            "version": "0.21"
+        },
+        "python": {
+            "full": "3.6.5 (default, May  5 2018, 03:07:21) \n[GCC 6.3.0 20170516]",
+            "version": "3.6.5"
+        },
+        "sqlite": {
+            "extensions": {
+                "json1": null
+            },
+            "fts_versions": [
+                "FTS4",
+                "FTS3"
+            ],
+            "version": "3.16.2"
+        }
+    }
+
+/-/plugins
+----------
+
+Shows a list of currently installed plugins and their versions. Example::
+
+    [
+        {
+            "name": "datasette_cluster_map",
+            "static": true,
+            "templates": false,
+            "version": "0.4"
+        },
+        {
+            "name": "datasette_plugin_demos",
+            "static": false,
+            "templates": true,
+            "version": "0.3"
+        }
+    ]
+
+/-/config
+---------
+
+Shows the :ref:`config` options for this instance of Datasette. `Config example <https://fivethirtyeight.datasettes.com/-/config>`_::
+
+    {
+        "default_facet_size": 30,
+        "default_page_size": 100,
+        "facet_suggest_time_limit_ms": 50,
+        "facet_time_limit_ms": 1000,
+        "max_returned_rows": 1000,
+        "sql_time_limit_ms": 1000
+    }