misc: add command to run prettier on docs (#2102)

* misc: add command to run prettier on docs

* Fix GH issue template

* Fix tests

* Add prettier-docs command to precommit

docs/api-doc-markdown.md

@@ -25,6 +25,7 @@ id: doc1
 title: My Document
 sidebar_label: Document
 ---
+
 ```
 
 Versioned documents have their ids altered to include the version number when they get copied. The new `id` is `version-${version}-${id}` where `${version}` is the version number of that document and `${id}` is the original `id`. Additionally, versioned documents get an added `original_id` field with the original document id.
@@ -38,6 +39,7 @@ title: My Document
 sidebar_label: Document
 original_id: doc1
 ---
+
 ```
 
 `custom_edit_url`: The URL for editing this document. If this field is not present, the document's edit URL will fall back to `editUrl` from optional fields of `siteConfig.js`. See [siteConfig.js](api-site-config.md) docs for more information.
@@ -50,6 +52,7 @@ id: doc-markdown
 title: Markdown Features
 custom_edit_url: https://github.com/facebook/docusaurus/edit/master/docs/api-doc-markdown.md
 ---
+
 ```
 
 ### Blog Posts
@@ -73,6 +76,7 @@ author: Frank Li
 authorURL: http://twitter.com/franchementli
 authorFBID: 100002976521003
 ---
+
 ```
 
 ## Extra Features
@@ -130,7 +134,6 @@ will lead to a table of contents of the functions:
 
 and each function will link to their corresponding sections in the page.
 
-
 ### Language-specific Code Tabs
 
 Display code in multiple programming languages using code tabs. First, mark the start and end of a code tabs group, by using `<!-- DOCUSAURUS_CODE_TABS -->` and `<!-- END_DOCUSAURUS_CODE_TABS -->` respectively in your markdown. Then start each tab with `<!--[TAB_TITLE]-->`.
@@ -144,26 +147,30 @@ produces this:
 <!--DOCUSAURUS_CODE_TABS-->
 
 <!--JavaScript-->
+
 ```js
 console.log('Hello, world!');
 ```
 
 <!--Python-->
+
 ```py
 print('Hello, world!')
 ```
 
 <!--C-->
+
 ```C
 #include <stdio.h>
 
 int main() {
-   printf("Hello World!");
-   return 0;
+  printf("Hello World!");
+  return 0;
 }
 ```
 
 <!--Pascal-->
+
 ```Pascal
 program HelloWorld;
 begin