add holidays instructions to readme

readme.md

@@ -174,3 +174,21 @@ server {
 ```
   - extract static files and make them available via nginx: `./manage.py collectstatic`
   - you start application by starting gunicorn and nginx: `service gunicorn start`, `service nginx start`
+
+## Operations
+
+### Public holidays
+
+to import public holidays run:
+
+```
+./manage.py holidays ${YEARS}
+```
+
+where ${YEARS} should be a space separated list of years for which the holidays will be imported.
+
+example:
+
+```
+./manage.py holidays 2017 2018 2019
+```
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