API/ABI Evolution Guideline: Clarify when to increase MAJOR

Any ABI incompatible change also requires to increase MAJOR,
because it makes versions not interchangeable.

Signed-off-by: Dylan Aïssi <dylan.aissi@collabora.com>

content/guides/api-abi_evolution_guideline.md

@@ -121,7 +121,7 @@ built time (*libfoo.so.2.4*) as long as the major (ABI) version is the same.
 The schema versioning is defined in the [Semantic Versioning Specification](https://semver.org/).
 **SemVer** is a common way to handle versioning. Basically, a version number
 contains three components *MAJOR*.*MINOR*.*PATCH*:
-- *MAJOR* version when you make incompatible API changes.
+- *MAJOR* version when you make incompatible API/ABI changes.
 - *MINOR* version when you add functionality in a backwards compatible manner.
 - *PATCH* version when you make backwards compatible bug fixes.