Added information about using github action (alshedivat#1226)

By using this Github action it is possible to keep the derived
repository up-to-date with its template.

I am currently using this to keep my website up to date with the
template repository. An example of the PR this action creates can be
seen [here](george-gca/george-gca.github.io#13).

Signed-off-by: George Araújo <[email protected]>

Author: george-gca

README.md

@@ -1,3 +1,3 @@
 version https://git-lfs.github.com/spec/v1
-oid sha256:3fd33735a2cfef8702ee7b4f8ffe9d3b157e0f96ae4657e2030352a16406c21d
-size 32890
+oid sha256:d35b95fa321f271f5c063b9046972aa930dd941655d41d58c80fb150830a6654
+size 33775