Added changelog and instructions

json_schema/README.md

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+## Changelog
+
+In this folder, there is a file named `changelog.json`. This file collects all the changes made to the JSON schemas.
+There is a JSON schema defining how the file is structured, under system/changelog.json. The main structure and goals
+of each part are:
+
+```json
+{
+  "<schema_path>": {
+    "current": "<current_version_of_schema>",
+    "changes": [
+      {
+        "from": "<previous published schema version>",
+        "to": "<Published schema version from which these changes are applicable>",
+        "minor": "<null||array. null if no changes of this type; array if changes. See 'major'>",
+        "major": [
+          {
+            "addition": "<null||object>. null if no change of this type. see 'update'",
+            "deletion": "<null||object>. null if no change of this type. see 'update'",
+            "update": {
+              "field": ["<field_name>", "<additional path(e.g. 'title', 'examples', 'items')>"],
+              "type": "<name||value. `name` updates the property `field` points to; `value` updates the value of that property>",
+              "new_value": "<new_value>"
+            }
+          }
+        ]
+      }
+    ]
+  }
+}
+
+```
+* Any element of the structure above that is enclosed by `<>` is variable. Any element not enclosed is fixed.
+* Each element of the `changes` array:
+  * Is an `object` with the following keys: `from`, `to`, `minor`, `major` (Skipping patch - Not needed to migrate a document)
+  * Represents a **published schema**, meaning you can apply each change separately to get to a specific schema version
+  * For `patch` changes, `minor` and `major` fields are left as null. It seems redundant, but when building a story to update a document from
+    e.g. 1.1.0 to 2.5.2, you need to collect all versions to be able to correctly parse the `changes` array.
+* This document does not fully collect how the schema itself evolves, but rather focuses how documents need to evolve.
+  Difficult cases such as adding required fields are not explicitly collected, but rather implied from the fact that
+  they are catalogued as additions in a `major` update.
+
+### Migration tips
+
+1. Only major changes are needed to migrate a document. You can ignore `patch` and `minor`, as these are just flavours
+   to increase the amount of metadata collected. `minor` and `patch` update collection may be important for non-validation
+   services (e.g. a `spreadsheet generator`)
+2. `update` changes are, _technically_, always automatically applicable. For changes that are not (e.g. substituting a
+   field for another one that is drastically different with different values, etc), please apply a `deletion` and 
+   `addition` operation 

json_schema/changelog.json

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+{
+  "last_update_date": "2024-10-15T13:43:00Z",
+  "system": {
+      "document": {
+        "current": "1.0.0",
+        "changes": []
+      }
+    },
+  "type": {
+    "project": {
+      "study": {
+        "current": "1.0.0",
+        "changes": []
+      }
+    },
+    "biomaterial": {
+      "clonal_cell_line": {
+        "current": "1.0.0",
+        "changes": []
+      },
+      "differentiated_product": {
+        "current": "2.0.0",
+        "changes": [
+          {
+            "from": "1.0.0",
+            "to": "2.0.0",
+            "minor": null,
+            "major": {
+              "addition": null,
+              "deletion": null,
+              "update": [
+                {
+                  "field": ["terminally_differentiated"],
+                  "type": "name",
+                  "new_value": "final_timepoint"
+                }
+              ]
+            }
+          }
+        ]
+      },
+      "library_preparation": {
+        "current": "2.0.0",
+        "changes": [
+          {
+            "from": "1.0.0",
+            "to": "2.0.0",
+            "minor": null,
+            "major": {
+              "addition": null,
+              "deletion": null,
+              "update": [
+                {
+                  "field": ["pcr_cycles"],
+                  "type": "name",
+                  "new_value": "cdna_pcr_cycles"
+                },
+                {
+                  "field": ["pcr_cycles_for_sample_index"],
+                  "type": "name",
+                  "new_value": "pcr_cycles_for_indexing"
+                }
+              ]
+            }
+          }
+        ]
+      },
+      "undifferentiated_product": {
+        "current": "1.0.0",
+        "changes": []
+      }
+    },
+    "file": {
+      "analysis_file": {
+        "current": "1.0.0",
+        "changes": []
+      },
+      "sequence_file": {
+        "current": "1.1.0",
+        "changes": [
+          {
+            "from": "1.0.0",
+            "to": "1.1.0",
+            "minor": {
+              "addition": [
+                {
+                  "field": ["run_id"],
+                  "type": "name"
+                }
+              ],
+              "deletion": null,
+              "update": null
+            },
+            "major": null
+          }
+        ]
+      }
+    },
+    "protocol": {
+      "expression_alteration": {
+        "current": "1.0.0",
+        "changes": []
+      }
+    }
+  }
+}
+