Improve the instructions on how to build the docs (#56018)

Summary:
This PR includes:

- A formatting change to make katex installation instructions more visible for Facebook employees.
- A short tip about how to start a lightweight HTTP server on a remote machine to browse the doc build artifacts.

Pull Request resolved: https://github.com/pytorch/pytorch/pull/56018

Reviewed By: H-Huang

Differential Revision: D27765157

Pulled By: cbalioglu

fbshipit-source-id: 67663de0ba7b742e0deb5358d1e45eea9edd840f

CONTRIBUTING.md

@@ -411,8 +411,12 @@ pip install -r requirements.txt
 # npm install -g katex
 # Or if you prefer an uncontaminated global executable environment or do not want to go through the node configuration:
 # npm install katex && export PATH="$PATH:$(pwd)/node_modules/.bin"
-# If you're a Facebook employee using a devserver, yarn may be more convenient:
-# yarn global add katex
+```
+
+> Note that if you are a Facebook employee using a devserver, yarn may be more convenient to install katex:
+
+```
+yarn global add katex
 ```
 
 3. Generate the documentation HTML files. The generated files will be in `docs/build/html`.
@@ -478,6 +482,13 @@ et my_machine -t="8000:8000"
 
 Then navigate to `localhost:8000` in your web browser.
 
+**Tip:**
+You can start a lightweight HTTP server on the remote machine with:
+
+```
+python -m http.server 8000 <path_to_html_output>
+```
+
 Alternatively, you can run `rsync` on your local machine to copy the files from
 your remote machine:
 ```bash