docs: Add documentation for codegen plugins (sqlc-dev#1904)

docs/reference/config.md

@@ -1,7 +1,7 @@
 # Configuration
 
-The `sqlc` tool is configured via a `sqlc.yaml` or `sqlc.json` file. This file must be
-in the directory where the `sqlc` command is run.
+The `sqlc` tool is configured via a `sqlc.yaml` or `sqlc.json` file. This
+file must be in the directory where the `sqlc` command is run.
 
 ## Version 2
 
@@ -34,10 +34,44 @@ Each mapping in the `sql` collection has the following keys:
   - Directory of SQL migrations or path to single SQL file; or a list of paths.
 - `queries`:
   - Directory of SQL queries or path to single SQL file; or a list of paths.
+- `codegen`:
+  - A colleciton of mappings to configure code generators. See [codegen](#codegen) for the supported keys.
 - `gen`:
   - A mapping to configure built-in code generators. See [gen](#gen) for the supported keys.
 - `strict_function_checks`
   - If true, return an error if a called SQL function does not exist. Defaults to `false`.
+  - 
+### codegen
+
+The `codegen` mapping supports the following keys:
+
+- `out`:
+  - Output directory for generated code.
+- `plugin`:
+  - The name of the plugin. Must be defined in the `plugins` collection.
+- `options`:
+  - A mapping of plugin-specific options.
+
+```yaml
+version: '2'
+plugins:
+- name: py
+  wasm:
+    url: https://github.com/tabbed/sqlc-gen-python/releases/download/v0.16.0-alpha/sqlc-gen-python.wasm
+    sha256: 428476c7408fd4c032da4ec74e8a7344f4fa75e0f98a5a3302f238283b9b95f2
+sql:
+- schema: "schema.sql"
+  queries: "query.sql"
+  engine: postgresql
+  codegen:
+  - out: src/authors
+    plugin: py
+    options:
+      package: authors
+      emit_sync_querier: true
+      emit_async_querier: true
+      query_parameter_limit: 5
+```
 
 ### gen
 
@@ -223,10 +257,27 @@ Each mapping in the `plugins` collection has the following keys:
 
 - `name`:
   - The name of this plugin. Required
-- `process`:
+- `process`: A mapping with a single `cmd` key
   - `cmd`:
     - The executable to call when using this plugin
-
+- `wasm`: A mapping with a two keys `url` and `sha256`
+  - `url`:
+    - The URL to fetch the WASM file. Supports the `https://` or `file://` schemes.
+  - `sha256`
+    - The SHA256 checksum for the downloaded file.
+
+```yaml
+version: 2
+plugins:
+- name: "py"
+  wasm: 
+    url: "https://github.com/tabbed/sqlc-gen-python/releases/download/v0.16.0-alpha/sqlc-gen-python.wasm"
+    sha256: "428476c7408fd4c032da4ec74e8a7344f4fa75e0f98a5a3302f238283b9b95f2"
+- name: "js"
+  process: 
+    cmd: "sqlc-gen-json"
+```
+
 ### global overrides
 
 Sometimes, the same configuration must be done across various specfications of code generation.

examples/python/sqlc.json

@@ -6,7 +6,7 @@
       "wasm": {
         "url": "https://github.com/tabbed/sqlc-gen-python/releases/download/v0.16.0-alpha/sqlc-gen-python.wasm",
         "sha256": "428476c7408fd4c032da4ec74e8a7344f4fa75e0f98a5a3302f238283b9b95f2"
-      },
+      }
     }
   ],
   "sql": [