add tables to data docu
@@ -56,6 +56,35 @@ to load IACT data. E.g. an alternative way to load the events for observation ID
data_store = DataStore.from_dir('$GAMMAPY_DATA/hess-dl3-dr1')
events = data_store.obs(23523).events
+The index tables
+================
+A typical way to organize the files relevant to the observation are the index tables.
+There are two relevant tables:
+
+- Observation index table: this table has information on specifics of each observation or run, meta data about each observation run,
+such as the pointing direction, the duration, the run ID...
+- HDU index table: this table links each of the observations listed in the observation
+index table to the relevant data and instrument response files.
+
+A `~gammapy.data.DataStore` can be created by giving each of these two tables separately, as well as the directory that they can be found in:
+
+.. testcode::
+
+ from gammapy.data import DataStore
+ directory = "$GAMMAPY_DATA/hess-dl3-dr1"
+ hdu_table_path = directory + "/hdu-index.fits.gz"
+ obs_table_path = directory + "/obs-index.fits.gz"
+
+ # separate tables
+ data_store = DataStore(hdu_table=hdu_table_path, obs_table=obs_table_path)
+
+ # directly from directory
+ data_store = DataStore.from_dir(directory)
+
+
+More details on these tables and their content can be found in https://gamma-astro-data-formats.readthedocs.io/en/latest/data_storage/index.html.
+
+
Working with event lists
========================
To take a quick look at the events inside the list, one can use `~gammapy.data.EventList.peek()`
