Update README.md

switched the branch in the docs from `master` to `main`

README.md

@@ -9,7 +9,7 @@ InCommon Incident Handling Framework document in asciidoc format
 ```
 asciidoctor main.adoc -o docs/index.html
 git commit docs/index.html
-git push origin master
+git push origin main
 ```
 To view the rendered HTML, visit: https://github.internet2.edu/pages/internet2/inc-incident-handling-fx/  
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