Add documentation for data import

docs/admin/import.md

@@ -4,5 +4,88 @@ title: Importing Data
 
 ## Importing Data
 
-!!! missing "TODO"
-	This section requires further work
+External data can be imported via the admin interface, allowing for rapid integration of existing datasets, or bulk editing of table data.
+
+!!! danger "Danger"
+    Uploading bulk data directly is a non-reversible action.
+
+!!! warning "Backup"
+    Ensure you have made a backup of your database before performing bulk data import.
+
+!!! warning "Supported Models"
+    Not all models in the InvenTree database support bulk import actions.
+
+When viewing a model (which supports bulk data import) in the admin interface, select the "Import" button in the top-right corner:
+
+{% with id="import", url="admin/import.png", description="Data import" %}
+{% include 'img.html' %}
+{% endwith %}
+
+The next screen displays a list of column headings which are expected to be present in the uploaded data file.
+
+{% with id="import_upload", url="admin/import_upload.png", description="Data upload" %}
+{% include 'img.html' %}
+{% endwith %}
+
+Select the data file to import, and the data format. Press the "Submit" button to upload the file.
+
+### File Format
+
+The uploaded data file must meet a number of formatting requirements for successful data upload. A simple way of ensuring that the file format is correct is to first [export data](../export) for the model in question, and delete all data rows (not the header row) from the exported data file.
+
+Then, the same file can be used as a template for uploading more data to the server.
+
+### ID Field
+
+The uploaded data file requires a special field called `id`. This `id` field uniquely identifies each entry in the database table(s) - it is also known as a *primary key*.
+
+The `id` column **must** be present in an uploaded data file, as it is required to know how to process the incoming data.
+
+Depending on the value of the `id` field in each row, InvenTree will attempt to either insert a new record into the database, or update an existing one.
+
+#### Empty ID
+
+If the `id` field in a given data row is empty (blank), then InvenTree interprets that particular row as a *new* entry which will be inserted into the database.
+
+If you wish for a new database entry to be created for a particular data row, the `id` field **must** be left blank for that row.
+
+#### Non-Empty ID
+
+If the `id` field in a given data row is *not* empty, then InvenTree inteprets that particular row as an *existing* row to override / update.
+
+In this case, InvenTree will search the database for an entry with the matching `id`. If a matching entry is found, then the entry is updated with the provided data.
+
+However, if an entry is *not* found with the matching `id`, InvenTree will return an error message, as it cannot find the matching database entry to update.
+
+!!! warning "Check id Value"
+    Exercise caution when uploading data with the `id` field specified!   
+
+### Import Preview
+
+After the data file has been uploaded and validated, the user is presented with a *preview* screen, showing the records that will be inserted or updated in the database.
+
+Here the user has a final chance to review the data upload.
+
+Press the *Confirm Import* button to actually perform the import process and commit the data into the database.
+
+{% with id="import_preview", url="admin/import_preview.png", description="Data upload preview" %}
+{% include 'img.html' %}
+{% endwith %}
+
+Note that *new* records are automatically assigned an `id` value.
+
+## Import Errors
+
+Manually importing data in a relational database is a complex process. You may be presented with an error message which describes why the data could not be imported.
+
+The error message should contain enough information to manually edit the data file to fix the problem.
+
+Any error messages are displayed per row, and you can hover the mouse over the particular error message to view specific error details:
+
+{% with id="import_error", url="admin/import_error.png", description="Data upload error" %}
+{% include 'img.html' %}
+{% endwith %}
+
+
+!!! info "Report Issue"
+    If the error message does not provide enough information, or the error seems like a bug caused by InvenTree itself, report an [issue on Github](https://github.com/inventree/inventree/issues).