chore: Use prefix 'vault' for changes to sample vault (#997)

* chore: Use prefix vault for any changes to sample vault

* chore: Add link to the sample vault

Author: claremacrae

.github/pull_request_template.md

@@ -27,7 +27,7 @@ Changes visible to users:
 - [ ] **New feature** (prefix: `feat` - non-breaking change which adds functionality)
 - [ ] **Breaking change** (prefix: `feat!!` or `fix!!` - fix or feature that would cause existing functionality to not work as expected)
 - [ ] **Documentation** (prefix: `docs` - improvements to any documentation content)
-- [ ] **Sample vault** (prefix: `sample` - improvements to the sample vault)
+- [ ] **Sample vault** (prefix: `vault` - improvements to the [Tasks-Demo sample vault](https://github.com/obsidian-tasks-group/obsidian-tasks/tree/main/resources/sample_vaults/Tasks-Demo))
 
 Internal changes: