readme: document versioning and stability expectations

References: https://gitlab.freedesktop.org/emersion/libdisplay-info/-/issues/13
Signed-off-by: Simon Ser <[email protected]>
diff --git a/README.md b/README.md
index 745d6fb..1ce95db 100644
--- a/README.md
+++ b/README.md
@@ -24,6 +24,8 @@
 This policy is aimed to propagate best practises when interpreting EDID
 and DisplayID information which can often be cryptic or even inconsistent.
 
+libdisplay-info uses [semantic versioning]. The public API is not yet stable.
+
 ## Contributing
 
 Open issues and merge requests on the [GitLab project].
@@ -67,6 +69,7 @@
     afl-fuzz -i test/data/ -o afl/ build/di-edid-decode/di-edid-decode
 
 [website]: https://emersion.pages.freedesktop.org/libdisplay-info/
+[semantic versioning]: https://semver.org/
 [GitLab project]: https://gitlab.freedesktop.org/emersion/libdisplay-info
 [Wayland contribution guidelines]: https://gitlab.freedesktop.org/wayland/wayland/-/blob/main/CONTRIBUTING.md
 [Developer Certificate of Origin 1.1]: https://developercertificate.org/