added template for Splunk apps

Co-Authored-By: Edward Courtemanche <edwardcourt@users.noreply.github.com>

community/Splunk.gitignore

+# gitignore template for Splunk apps
+# documentation: http://docs.splunk.com/Documentation/Splunk/6.2.3/admin/Defaultmetaconf
+
+# Splunk local meta file
+local.meta
+
+# Splunk local folder
+local