README: add "HOWTO: Work with images"

README.md

@@ -8,6 +8,25 @@ you have Hugo installed, clone the repo, and run:
 $ hugo server
 ```
 
+## HOWTO: Work with images
+
+Simple! You can use all common formats: `.png`, `.jpg` or `.svg`; just make
+sure the images are high quality. For `.png` and `.jpg`, they should be more
+than `1400px` wide. If you can't find such a high-resolution image then use
+the best quality you can find. Put the image in the same folder as your post,
+and embed them in the post content like this:
+
+```markdown
+![Image description](image-file.png)
+```
+Please note that the image description is required. It should be a meaningful
+explanation of what is shown on the image, which will be put into the
+`<img alt="...">` attribute (important for SEO).
+
+You don't have to do any image processing besides finding high-quality images.
+The blog will automatically generate smaller previews and convert them to
+alternative formats such as `WebP` for faster rendering.
+
 ## HOWTO: Publish a draft blog post
 
 Add the following two lines in the Frontmatter markup at the beginning of the