Update README.md

Hash checksum added.

README.md

@@ -18,6 +18,33 @@ The **NASA Knowledge Graph Dataset** is an expansive graph-based dataset designe
 
 The primary goal of the NASA Knowledge Graph is to bridge scientific publications with the datasets they reference, facilitating deeper insights and research opportunities within NASA's scientific and data ecosystem. By organizing these interconnections within a graph structure, this dataset enables advanced analyses, such as discovering influential datasets, understanding research trends, and exploring scientific collaborations.
 
+## Data Integrity
+
+Each file in the dataset has a SHA-256 checksum to verify its integrity:
+
+| File Name                  | SHA-256 Checksum                                                          |
+|----------------------------|---------------------------------------------------------------------------|
+| `graph.cypher`             | `9159a04d385ccbd53858eaf21f4f80c9ce17b52ff997c410400ecc085bfbe010`        |
+| `graph.graphml`            | `2ca75302371f6be9fee1a051948144ba26147c1eebaea1e7a00dd1eb86ba2031`        |
+| `graph.json`               | `1dbeef75206edc3f893819589461b2a2ed9c1a14311dcc8aca304fb58c005ca1`        |
+
+### Verification
+
+To verify the integrity of each file, calculate its SHA-256 checksum and compare it with the hashes provided above.
+
+You can use the following Python code to calculate the SHA-256 checksum:
+```python
+import hashlib
+
+def calculate_sha256(filepath):
+    sha256_hash = hashlib.sha256()
+    with open(filepath, "rb") as f:
+        for byte_block in iter(lambda: f.read(4096), b""):
+            sha256_hash.update(byte_block)
+    return sha256_hash.hexdigest()
+```
+
+
 ## Dataset Structure
 
 ### Nodes and Properties