improve specification versioning

Signed-off-by: Onur Özkan <work@onurozkan.dev>

README.md

@@ -28,7 +28,10 @@ The repository is currently in infrastructure setup. Formal project specificatio
 
 Formal specs should be colocated with the code or board package they govern.
 
-- Implementation-linked specs should use versioned sidecar filenames such as `control_loop.v0.1.0.spec.md` next to the related module or package.
+- Implementation-linked specs should use stable sidecar filenames such as `control_loop.spec.md` next to the related module or package.
+- Version history should live inside the same spec file as additional spec entries, not in the filename.
+- Each appended spec entry should begin with version marker such as `# --- version: 0.1.0 ---`.
+- Inside a spec entry, `#` is reserved for version markers and content headings should start at `##`.
 - Rust items should link to those sidecar specs through `#[spec("...")]`.
 - Missing linked spec files must fail compilation.
 
@@ -37,6 +40,6 @@ Example:
 ```rust
 use kaptan_spec::spec;
 
-#[spec("control_loop.v0.1.0.spec.md")]
+#[spec("control_loop.spec.md")]
 pub struct ControlLoop;
 ```