Add README.md and DEVEL.md .

DEVEL.md

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+## Useful links
+
+Writing plugins:
+
+* [Getting involved with calibre](https://calibre-ebook.com/get-involved)
+* [Writing plugins](https://manual.calibre-ebook.com/creating_plugins.html)
+
+Environment:
+
+* [Since version 5.0 calibre uses python3.](https://calibre-ebook.com/new-in/fourteen)
+* [Since version 4.0 calibre has replaced Qt WebKit with Qt WebEngine.](https://calibre-ebook.com/new-in/thirteen)
+* [Since version 2.0 calibre uses Qt5.](https://calibre-ebook.com/new-in/eleven)
+
+## Release process
+
+    cd REPO_ROOT
+    VERSION="1.1.0"
+    cd theanarchistlibrary_store
+    zip ../releases/theanarchistlibrary_store_v${VERSION}.zip *

README.md

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+# calibre plugin for accessing theanarchistlibrary.org
+
+## Introduction
+
+[calibre](https://calibre-ebook.com) is an ebook management software.
+It can be extended through plugins.
+
+The plugin *theanarchistlibrary_store* adds
+[theanarchistlibrary.org](https://theanarchistlibrary.org)
+as ebook "Store". It allows to search and download
+items from theanarchistlibrary.org from within calibre.
+
+## Usage
+
+See [there](https://bookshelf.theanarchistlibrary.org/library/calibre-store-plugin).
+
+## Compatibility
+
+This plugin has been tested with calibre 3.39.1 and calibre 5.7.2 on linux on arm64.
+It is expected to work with other versions and on other operating systems and platforms.