Start a simple style guide

The specifications could benefit from listing some simple style rules such as

```quote
* Use "work-group", not "workgroup" or "work group".
* Use dictionary entries for API entry point, i.e. `{clEntryName}`, not `clEntryName`.
```

The Vulkan specification has an extensive style guide [1], which is a great thing to aspire too, but to start I just mean a `styleguide.txt` that lists simple rules and guidelines. Focusing on things that sometimes end up being inconsistent.

[1] https://www.khronos.org/registry/vulkan/specs/1.2/styleguide.html

Review the specification sources and the Vulkan style guide linked in the issue before creating the proposed styleguide.txt. Collect recurring inconsistencies such as terminology and API-entry-point formatting, then document a focused initial set of rules; done means the file exists and its guidance is clear and consistent.

Written by the indexing model from the issue text.