readme for plugins

Author: hatton

README.md

@@ -129,3 +129,7 @@ Options:
 | -i, --img-output-path <string>        |           | Path to directory where images will be stored. If this is not included, images will be placed in the same directory as the document that uses them, which then allows for localization of screenshots.             |
 | -p, --img-prefix-in-markdown <string> |           | When referencing an image from markdown, prefix with this path instead of the full img-output-path. Should be used only in conjunction with --img-output-path.                                                     |
 | -h, --help                            |           | display help for command                                                                                                                                                                                           |
+
+# Plugins
+
+If your project needs some processing that docu-notion doesn't already provide, you can provide a plugin that does it. See the [plugin readme](src/plugins/README.md).

src/plugins/README.md

@@ -0,0 +1,37 @@
+# Plugins (Advanced & Experimental)
+
+If your project needs some processing that docu-notion doesn't already provide, you can provide a plugin that does it. If there is call for it, we'll add more documentation in the future. But for now, here's the steps:
+
+1. Add a `docu-notion.config.ts` to the root level of your project directory.
+1. Add something like this:
+
+```
+import { IDocuNotionConfig } from "docu-notion";
+
+const config: IDocuNotionConfig = {
+  plugins: [bloomBookEmbedding],
+};
+const dummyMarkdownModifier: IPlugin = {
+  name: "dummyMarkdownModifier",
+
+  regexMarkdownModifications: [
+    {
+      regex: /aaa(.*)aaa/,
+      replacementPattern: "bbb$1bbb",
+    },
+  ],
+};
+const config: IDocuNotionConfig = {
+  plugins: [dummyMarkdownModifier],
+};
+export default config;
+
+```
+
+For other available plugin points, see [pluginTypes.ts](pluginTypes.ts). All of the built-in processing is also done via built-in plugins, so those files and their unit tests should serve as good examples.
+
+Once you have your plugin working, you have three options:
+
+- just keep it as part of your Docusaurus project.
+- publish it to NPM so that others can use it. Let us know so that we can advertise it here.
+- talk to us about making it a built-in part of `docu-notion`