docs/manual/adding-packages-meson.adoc: fix occurrences typo

Occurrences is with double-c-double-r.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

docs/manual/adding-packages-meson.adoc

@@ -61,7 +61,7 @@ added to +FOO_DEPENDENCIES+. Note that the support for +baz+ is explicitly
 disabled at line 20, if the package is not selected.
 
 To sum it up, to add a new meson-based package, the Makefile example can be
-copied verbatim then edited to replace all occurences of +FOO+ with the
+copied verbatim then edited to replace all occurrences of +FOO+ with the
 uppercase name of the new package and update the values of the standard
 variables.