Fix Scatter Spec Diagram (#2746)

fixes #2744

The change is the label of the 4th column of the table from

```
Full start index: 
scatter start index via scatter_dims_to_operand_dims = [0, 1]   
```

to

```
Full start index: 
scatter start index via scatter_dims_to_operand_dims = [2, 1]   
```

Author: sdasgup3

docs/images/spec/README.md

@@ -0,0 +1,19 @@
+# Image Source and Update Policy
+
+The Google slides located at [OpenXLA community
+drive](https://docs.google.com/presentation/d/1vr6x3VtV77NPIwR26uiHEJQb407QtRXMUfIi5CSs8aA/edit?usp=drive_link)
+is considered the source of truth for the SVG images contained within this
+directory. These images were downloaded in SVG format to facilitate their
+integration into this project.
+
+For any community-approved modifications or updates, please adhere to the
+following procedure:
+
+1. Create a copy of the source presentation linked above. Implement your
+proposed edits within this copy.
+2. Export the revised image(s) from your edited presentation as SVG files.
+Submit these SVG files, along with a link to your forked presentation, as part
+of a pull request for review.
+3. Upon approval of your PR, a maintainer will merge the submitted SVG files
+into this directory. Simultaneously, the maintainer will merge the changes from
+your forked presentation into the original source presentation.