docs: update README.md

Author: github-actions[bot]

README.md

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+# php-devcontainer
+
+> A custom devcontainer image suited for Php development.
+
+## Supported tags
+
+- <no value>
+
+## Contents
+
+### Tools
+
+- zsh
+- [atuin](https://atuin.sh/)
+- [starship](https://starship.rs/)
+- composer
+- nano
+
+### Php Extensions
+
+- xdebug
+- pgsql
+- pdo_pgsql
+- redis
+- opcache
+- pcntl
+- zip
+- intl