DOC-516 | Extend new toolchain README

MIGRATE.md

@@ -0,0 +1,42 @@
+# Migration to Hugo docs toolchain
+
+The migration script converts the Jekyll-specific Markdown files as well as
+the DocuBlocks from the main repository to the Hugo-specific Markdown files
+that are needed for the new documentation toolchain.
+
+## Prerequisites
+
+- **docker-compose**
+- **Python 3**
+
+## How to run the migration script
+
+Create a dedicated folder for testing the migration process.
+
+**Setup**
+
+```shell
+.> git clone [email protected]:arangodb/docs-hugo.git
+.> cd docs-hugo
+docs-hugo> cd migration-tools
+docs-hugo/migration-tools> pip3 install pyyaml commonmark python-frontmatter
+```
+
+**Execute migration**
+
+```shell
+docs-hugo/migration-tools> ./migration.sh migrate <docsOld> <docsNew> <docublocks> <version>
+```
+
+- `docsOld`: input path to the old toolchain and content in Jekyll's format,
+  pointing to the root of the `arangodb/docs` working copy
+
+- `docsNew`: output path for the new toolchain and content in Hugo's format,
+  pointing to the root of the `arangodb/docs-hugo` working copy
+  (not including `/site/content`)
+
+- `docublocks`: input path to a working copy of the `arangodb/arangodb`
+  repository, needed to read the old DocuBlocks
+
+- `version`: the version of the old content to migrate to the new toolchain,
+  indicating a version folder like `3.11`