sc-70154-update-qml-readme-to-highlight-image-standards (#1184)

## Ticket
-
[sc-70154-update-qml-readme-to-highlight-image-standards](https://app.shortcut.com/xanaduai/story/70154/update-qml-readme-to-highlight-image-standards)

## Changes
- Add instructions to `README.md` about image standards to be followed
while writing demos this QML repository.
- Requirements sources from this
[doc](https://www.notion.so/xanaduai/Image-standards-for-web-projects-264c09e45a8941a597918b878a2f1a5e)
- Since QML is public & the notion doc is private (accessible by Xanadu
only) added the relevant standards in text form in the `README.md`

## Preview
-
https://github.com/PennyLaneAI/qml/blob/2e9da1bb2bef3cd8a2eb504459f686ab20b9ec0c/README.md

README.md

@@ -66,8 +66,23 @@ quantum computing paper/result.
 
   where `<demo name>` is a sub-directory with the name of
   your demo.
+  <details>
+    <summary><b>Follow these standards when adding images</b></summary>
+
+    ### File Size
+    * Always aim to keep the image file size in kilobytes (KB’s) 
+    * Always compress the image to the best possible size where quality is acceptable.
+
+    ### Formats
+    * Use `.png` for everything (decorative images, descriptive images, logos etc)
+    * Use `.gif` for animated images
+
+    ### Dimensions
+    * To maintain quality and performance, every image should be twice (2X) its visible dimension size on the web page, and at a minimum of `150 ppi/dpi` (preferably `300 ppi/dpi`).
+  </details><br>
 
 - Add and select an author photo from the `_static/authors` folder. The image name should be as `<author name>_<author surname>.<format>`. If this is a new author and their image is not a headshot, store the original image as `<author name>_<author surname>_original.<format>` and create a cropped headshot with the aforementioned name.
+
 - In the same folder create a `<author name>.txt` file where to include the bio following this structure:
 
   ```txt