docs: Update the local docs readme so that we can better run the docs locally (#1550)

Author: another-rex

docs/.bundle/config

@@ -0,0 +1,2 @@
+---
+BUNDLE_PATH: "vendor/bundle"

docs/Gemfile.lock

@@ -43,7 +43,7 @@ GEM
       logger
     faraday-net_http (3.3.0)
       net-http
-    ffi (1.17.0-x86_64-linux-gnu)
+    ffi (1.17.1)
     forwardable-extended (2.6.0)
     gemoji (4.1.0)
     github-pages (232)

docs/README.md

@@ -4,16 +4,24 @@ The [OSV-Scanner docs](https://google.github.io/osv-scanner) are hosted on a [Gi
 
 ## Running docs locally
 
-To run docs locally, you will need [Jekyll](https://jekyllrb.com/docs/installation/) on your machine.
+To run the docs locally:
 
-Here are other [pre-requisites] and instructions for running the [docs locally].
+- Install `ruby (>= 3.1.0)`. This should come with `bundler`.
+  - On Debian, you need to install them separately:
+    - `ruby`
+    - `ruby-bundler`
+- In this directory:
+  - `bundle config set --local path 'vendor/bundle'` (you can skip this step if serving from this directory, as the config is already saved in `.bundle/config`)
+  - `bundle install`
+  - `bundle exec jekyll serve`
+
+Here's the full documentation on github for running the [docs locally].
 
-[pre-requisites]: https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/testing-your-github-pages-site-locally-with-jekyll#prerequisites
 [docs locally]: https://docs.github.com/en/pages/setting-up-a-github-pages-site-with-jekyll/testing-your-github-pages-site-locally-with-jekyll#building-your-site-locally
 
 ## Formatting docs
 
-We use - [Prettier](https://prettier.io/) to standardize the format of markdown and config files.
+We use [Prettier](https://prettier.io/) to standardize the format of markdown and config files.
 
 This requires [node/npm](https://docs.npmjs.com/downloading-and-installing-node-js-and-npm) to be installed.