Update attach page

Author: kabilar

docs/src/design/tables/attach.md

@@ -1,57 +1,59 @@
-# File Attachment Datatype
+# External Data
 
-## Configuration & usage
+## File Attachment Datatype
 
-<!-- Since https://github.com/datajoint/datajoint-python/issues/480 -->
+### Configuration & Usage
 
-The `attach` attribute type allows users to `attach` files into DataJoint
+Corresponding to issue 
+[#480](https://github.com/datajoint/datajoint-python/issues/480), 
+the `attach` attribute type allows users to `attach` files into DataJoint
 schemas as DataJoint-managed files. This is in contrast to traditional `blobs`
 which are encodings of programming language data structures such as arrays.
 
 The functionality is modeled after email attachments, where users `attach`
-a file along with a message, and message recipients have access to a
+a file along with a message and message recipients have access to a
 copy of that file upon retrieval of the message.
 
 For DataJoint `attach` attributes, DataJoint will copy the input
-file into a DataJoint store, hashing the file contents and tracking
+file into a DataJoint store, hash the file contents, and track
 the input file name. Subsequent `fetch` operations will transfer a
-copy of the file to the local directory of the python process and
+copy of the file to the local directory of the Python process and
 return a pointer to it's location for subsequent client usage. This
 allows arbitrary files to be `uploaded` or `attached` to a DataJoint
 schema for later use in processing. File integrity is preserved by
-checksumming the data upon attachment and verifying the contents
+checksum comparison against the attachment data and verifying the contents
 during retrieval.
 
 For example, given a `localattach` store:
 
-```json
+```python
 dj.config['stores'] = {
-     'localattach': {
-     'protocol': 'file',
-     'location': '/data/attach',
-     }
+  'localattach': {
+    'protocol': 'file',
+    'location': '/data/attach'
+  }
 }
 ```
 
-A `ScanAttachment` table can be created::
+A `ScanAttachment` table can be created:
 
 ```python
 @schema
 class ScanAttachment(dj.Manual):
-     definition = """
-     -> Session
-     ---
-     scan_image:    attach@localattach  # attached image scans
-     """
+    definition = """
+    -> Session
+    ---
+    scan_image:    attach@localattach  # attached image scans
+    """
 ```
 
 Files can be added using an insert pointing to the source file:
 
 ```python
-ScanAttachment.insert1((0, '/input/image0.tif'))
+>>> ScanAttachment.insert1((0, '/input/image0.tif'))
 ```
 
-And then retrieved to the current directory using fetch:
+And then retrieved to the current directory using `fetch`:
 
 ```python
 >>> s0 = (ScanAttachment & {'session_id': 0}).fetch1()