chore(docs): restore dev docs

docs/Developer Guide/Developer Guide/Development and architecture/Synchronisation/Content hashing.md

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+# Content hashing
+Entity hashing is done in `content_hash#getEntityHashes`.
+
+*   It works by looking at the `entity_changes` table and going through each of the entity names/types:
+    *   `blobs`
+    *   `attributes`
+    *   `revisions`
+    *   `attachments`
+    *   `notes`
+    *   `branches`
+    *   `etapi_tokens`
+    *   `options`
+*   For some reason `note_reordering` entities are ignored specifically.
+*   All the rows in `entity_changes` are then ordered alphabetically, based on their `entityId`.
+*   Every entity row is then grouped by `entityName` and then by sector. The sector is defined as the first character of the `id`.
+*   The hash is altered to add the `isErased` value as well since the hash of deleted entries is not updated.
+*   For each sector, the hash is calculated using `utils.hash`, using SHA1 encoded as Base64.