Exclude a couple of files from being deployed to the Azure Function

Before we start deploying this GitHub App from its own repository, we
need to make sure that only the intended files will be deployed.

This is an almost verbatim copy (leaving out the `*.gif` line) from
https://github.com/dscho/leave-me-alone-github-app/blob/main/.funcignore

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Author: dscho

.funcignore

@@ -0,0 +1,4 @@
+/.*
+/*.md
+/host.json
+/local.settings.json