README: Re-phrase the mentioning of ABI

ABI (Application Binary Interface), can be a confusing term for
people who stumble over it. What we want to achieve is to let people
know that the interface is stable and backwards compatible.

README.md

@@ -22,8 +22,10 @@
 
 # Learn about CLAP
 
-CLAP stands for **CL**ever **A**udio **P**lugin.
-It is an audio plugin ABI which defines a standard for *Digital Audio Workstations* and audio plugins (synthesizers, audio effects, ...) to work together.
+CLAP stands for **CL**ever **A**udio **P**lugin. It is an *API* that provides a
+stable binary interface with backwards compatibility to define a standard for
+*Digital Audio Workstations* and audio plugins (synthesizers, audio effects,
+...) to work together.
 
 To work with CLAP, include [clap/clap.h](include/clap/clap.h).