feat(changelog): add version scoping section (#1)

Author: Tieske

CHANGELOG.md

@@ -1,10 +1,20 @@
 # CHANGELOG
 
+## Versioning
+
+This library is versioned based on Semantic Versioning ([SemVer](https://semver.org/)).
+
+#### Version scoping
+
+The scope of what is covered by the version number excludes:
+
+- error messages; the text of the messages can change, unless specifically documented.
+
 #### Releasing new versions
 
 - create a release branch
 - update the changelog below
-- update version and copyright-years in `./LICENSE` and `./src/[module-name]/init.lua` (in doc-comments
+- update version and copyright-years in `./LICENSE.md` and `./src/[module-name]/init.lua` (in doc-comments
   header, and in module constants)
 - create a new rockspec and update the version inside the new rockspec:<br/>
   `cp [module-name]-scm-1.rockspec ./rockspecs/[module-name]-X.Y.Z-1.rockspec`
@@ -18,6 +28,8 @@
 - test the newly created rock:<br/>
   `luarocks install [module-name]`
 
+## Version history
+
 ### Version X.Y.Z, unreleased
 
 - a fix

README.md

@@ -16,6 +16,6 @@ See [LICENSE.md](LICENSE.md)
 
 See [online documentation](https://[github-account-name].github.io/[repo-name]/)
 
-## Changelog
+## Changelog & Versioning
 
 See [CHANGELOG.md](CHANGELOG.md)