Add readme for docs (#65)

Author: sakirtemel

plantuml-docs/README.adoc

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+= PlantUML Alternative Docs
+
+PlantUML alternative docs for better readability using the alphadocs as a source.
+
+image::demo.png[]
+
+== Features
+
+- Better navigation, top for chapters, left for topics, right for subtopics
+
+- Lunr search engine
+
+- Better layout for docs based on Antora
+
+- Automated sync from link:http://alphadoc.plantuml.com[alphadoc]
+
+- Static pages, can be served on Github Pages or any CDN
+
+- Edit link taking to dokuwiki
+
+- Lazy loading diagrams
+
+- Clicking the diagram takes diagram editing
+
+== Antora structure
+
+- We have antora-playbook.yml that defines our site.
+
+- Our site uses only one component called docs.
+
+- docs component's pages are automatically generated in a PR after processing the docs_from_alphadoc. It shouldn't be edited manually.
+
+- Navigation is NOT generated automatically on purpose, it needs to be edited for the best convinence.
+
+- Site is built and pushed into gh-pages branch when a new commit is merged to main.
+
+== Updating the docs from alphadoc
+
+This project uses link:http://alphadoc.plantuml.com/toc/asciidoc/en[PlantUML's alphadoc] as a source of truth.
+
+To fetch the latest docs from alphadoc, `sync-docs` workflow should be manually triggered by
+ going to the link:../../../actions/workflows/sync-docs.yml[actions page] or calling it via API.
+It automatically creates a PR with the updated docs.