[doc] Disable auto-included addon-docs when adding GFM plugin

This fixes a confusing issue when you try to add the GFM plugin, when using `addon-essentials` (AFAIK, that's the default?): Storybook ignores the new plugin because the `docs` add-on was already included. Changing code order doesn't seem to help, either.

I only found the solution after digging through this old issue: #20091 (comment)

> **Note:** this should also be fixed for [v7](https://storybook.js.org/docs/7/writing-docs/mdx#anatomy-of-mdx), but I didn't find the correct branch to edit that - the "edit on GitHub" link simply takes me to `next`, where the v7 files don't exist anymore.

Author: igorsantos07

docs/_snippets/storybook-main-config-remark-options.md

@@ -7,6 +7,17 @@ export default {
   stories: ['../src/**/*.mdx', '../src/**/*.stories.@(js|jsx|mjs|ts|tsx)'],
   addons: [
     // Other addons go here
+
+    // If you have @storybook/addon-essentials enabled, change it to the following:
+    /*
+    {
+      name: "@storybook/addon-essentials",
+      options: {
+        docs: false,
+      },
+    },
+    */
+
     {
       name: '@storybook/addon-docs',
       options: {
@@ -32,6 +43,17 @@ const config: StorybookConfig = {
   stories: ['../src/**/*.mdx', '../src/**/*.stories.@(js|jsx|mjs|ts|tsx)'],
   addons: [
     // Other addons go here
+
+    // If you have @storybook/addon-essentials enabled, change it to the following:
+    /*
+    {
+      name: "@storybook/addon-essentials",
+      options: {
+        docs: false,
+      },
+    },
+    */
+
     {
       name: '@storybook/addon-docs',
       options: {