Update .gitignore to exclude virtual environment directories and enhance documentation on adding datasets with h5py

.gitignore

@@ -38,6 +38,11 @@ docs/build/
 docs/source/pynwb.*.rst
 
 
+# Virtual Environment
+venv/
+env/
+ENV/
+
 # setuptools
 build/
 dist/

docs/gallery/advanced_io/plot_editing.py

@@ -162,3 +162,41 @@
         "synthetic_timeseries_renamed",
         "/analysis/synthetic_timeseries_renamed",
     )
+
+##############################################
+# Adding datasets using h5py
+# --------------------------
+# You can also use h5py to add new datasets to existing groups. Here's an example of
+# adding a genotype dataset to the Subject object:
+
+from pynwb import NWBFile, NWBHDF5IO
+from pynwb.file import Subject
+import h5py
+from datetime import datetime
+
+# First, let's create a file with a Subject that is missing a genotype
+nwbfile = NWBFile(
+    session_description="example file with subject",
+    identifier="EXAMPLE_ID",
+    session_start_time=datetime.now(),
+    session_id="LONELYMTN",
+    subject=Subject(
+        subject_id="mouse001",
+        species="Mus musculus",
+        age="P30D",
+    )
+)
+
+with NWBHDF5IO("test_edit3.nwb", "w") as io:
+    io.write(nwbfile)
+
+# Now add a genotype dataset to the Subject using h5py
+with h5py.File("test_edit3.nwb", "r+") as f:
+    # Create the genotype dataset in the subject group
+    subject_group = f["general/subject"]
+    subject_group.create_dataset("genotype", data="Sst-IRES-Cre")
+
+# Verify the dataset was added
+with NWBHDF5IO("test_edit3.nwb", "r") as io:
+    nwbfile = io.read()
+    print(f"Subject genotype: {nwbfile.subject.genotype}")