📝(backend) add docs

i am documenting the index command

Signed-off-by: charles <charles.englebert@protonmail.com>

docs/commands/index.md

@@ -0,0 +1,69 @@
+# Index Command
+
+The `index` management command is used to index documents to the remote search indexer.
+
+It sends an asynchronous task to the Celery worker.
+
+## Usage
+
+### Make Command
+
+```bash
+# Basic usage with defaults
+make index
+
+# With custom parameters
+make index batch_size=200 lower_time_bound="2024-01-01T00:00:00"
+
+# All parameters
+make index batch_size=200 \
+  lower_time_bound="2024-01-01T00:00:00" \
+  upper_time_bound="2024-01-31T23:59:59" \
+```
+
+### Command line
+
+```bash
+python manage.py index \
+  --lower-time-bound "2024-01-01T00:00:00" \
+  --upper-time-bound "2024-01-31T23:59:59" \
+  --batch-size 200 \
+  --async_mode
+```
+
+### Django Admin
+
+The command is available in the Django admin interface:
+
+1. Go to `/admin/core/run-indexing/`, you arrive at the "Run Indexing Command" page
+3. Fill in the form with the desired parameters
+4. Click **"Run Indexing Command"**
+
+## Parameters
+
+### `--batch-size`
+- **type:** Integer
+- **default:** `settings.SEARCH_INDEXER_BATCH_SIZE`
+- **description:** Number of documents to process per batch. Higher values may improve performance but use more memory.
+
+### `--lower-time-bound`
+- **optional**: true
+- **type:** ISO 8601 datetime string
+- **default:** `None`
+- **description:** Only documents updated after this date will be indexed.
+
+### `--upper-time-bound`
+- **optional**: true
+- **type:** ISO 8601 datetime string
+- **default:** `None`
+- **description:** Only documents updated before this date will be indexed.
+
+## `--async_mode`
+- **type:** Boolean flag
+- **default:** `False`
+- **description:** Runs asynchronously is async_mode==True. 
+
+## Crash Safe Mode
+
+The command saves the updated.at of the last document of each successful batch into the `bulk-indexer-checkpoint` cache variable.
+If the process crashes, this value can be used as `lower-time-bound` to resume from the last successfully indexed document.