doc(tools): add basic README for tools folder

tools/README.md

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+# GeoNetwork-UI Tools
+
+This directory contains various tools used in the development and deployment phases of GeoNetwork-UI.
+
+## [`docker` folder](./docker)
+
+Contains a generic Dockerfile that can be used for any applications provided by GeoNetwork-UI, as well as the corresponding entrypoing and NGINX configuration file.
+
+## [`i18n` folder](./i18n)
+
+Contains utilities related to translation files used in GeoNetwork-UI.
+
+## [`pipelines` folder](./pipelines)
+
+Contains utilities related to [registering pipelines on ElasticSearch](https://www.elastic.co/guide/en/elasticsearch/reference/7.17/ingest.html). Pipelines are used to preprocess records during the indexation process, thus
+offering greater control over the values returned by ElasticSearch and giving an improved user experience when searching records.
+
+A CLI is provided to let you register or clear GeoNetwork-UI-related pipelines on an ES instance. For example:
+
+```shell
+node pipelines/regiser-es-pipelines.js register --host=http://localhost:9200 --records-index=gn-records
+```
+
+A docker image can also be built to register the pipelines automatically in a docker environment:
+
+```shell
+npm run pipelines:docker-build
+# once image is built, use it like so:
+docker run --rm --env ES_HOST=http://localhost:9200 --env RECORDS_INDEX=gn-records --network host geonetwork/geonetwork-ui-tools-pipelines
+```
+
+## [`webcomponent` folder](./webcomponent)
+
+Contains utilities related to Web Components provided by the GeoNetwork-UI project.
+
+## Other tools
+
+- `generate-api.sh`: regenerates API clients automatically from existing OpenAPI YAML files
+- `make-archive.sh`: bundles directories in `dist` and names it appropriately for releases
+- `print-docker-tag.sh`: outputs a docker tag based on the current git tag/branch