Spelling fixes

Spelling errors found using github.com/lucasdemarchi/codespell
A tool to fix common misspellings.
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Change-Id: I6dcf76a74487d04d4568d55d08d1b07f627e5e74
Signed-off-by: Gunnar Mills <gmills@us.ibm.com>
diff --git a/example/net/poettering/Calculator.interface.yaml b/example/net/poettering/Calculator.interface.yaml
index 7932aed..d289c21 100644
--- a/example/net/poettering/Calculator.interface.yaml
+++ b/example/net/poettering/Calculator.interface.yaml
@@ -1,5 +1,5 @@
 description: >
-    An example interface originally described as part of the announcment
+    An example interface originally described as part of the announcement
     of new sd-bus interfaces at:
         http://0pointer.net/blog/the-new-sd-bus-api-of-systemd.html
 methods: