add 3.2 api doc to index list

Author: jef-n

doc/index.dox

@@ -32,6 +32,7 @@ See \ref api_break for information about incompatible changes to API between rel
 
 Earlier versions of the documentation are also available on the QGIS
 website:
+<a href="https://qgis.org/api/3.2">3.2</a>,
 <a href="https://qgis.org/api/3.0">3.0</a>,
 <a href="https://qgis.org/api/2.18">2.18 (LTR)</a>,
 <a href="https://qgis.org/api/2.14">2.14 (LTR)</a>,