Add documentation on how to work with tags

docs/source/index.rst

@@ -12,6 +12,7 @@ files & metadata into self contained datasets.
    philosophy
    quick_start_guide
    working_with_datasets
+   tagging_datasets
    annotating_datasets
    working_with_overlays
    configuring_user_name_and_email

docs/source/tagging_datasets.rst

@@ -0,0 +1,27 @@
+Tagging datasets
+================
+
+It is possible to tag datasets with labels.
+
+To tag a dataset with the label "rnaseq" one would use the command below::
+
+    $ dtool tag set <DS_URI> rnaseq
+
+It is possible to add more than one tag to a dataset. The command below
+adds the tag "A.thaliana"::
+
+    $ dtool tag set <DS_URI> A.thaliana
+
+To list tags one would use the command below:
+
+    $ dtool tag ls <DS_URI>
+
+This would produce the output::
+
+    A.thalina
+    rnaseq
+
+It is possible to delete a tag that has been added to a dataset::
+
+
+    $ dtool tag delete <DS_URI> A.thaliana