README.md: add packaging status

Signed-off-by: Lukas Fleischer <lfleischer@calcurse.org>

README.md

@@ -1,17 +1,21 @@
-calcurse
-========
+# calcurse
 
 [![Build and test](https://github.com/lfos/calcurse/actions/workflows/make.yml/badge.svg)](https://github.com/lfos/calcurse/actions/workflows/make.yml)
 [![Lint Python](https://github.com/lfos/calcurse/actions/workflows/lint_python.yml/badge.svg)](https://github.com/lfos/calcurse/actions/workflows/lint_python.yml)
 
 ![Demo](https://calcurse.org/images/demo.gif)
 
-Building
---------
+## Installation
 
-Install the following build dependencies. If your distro segments development
-files from core packages (i.e., \*-devel or \*-dev packages), you may need to
-install those as well:
+calcurse is available on a number of Linux distributions:
+
+[![Packaging status](https://repology.org/badge/vertical-allrepos/calcurse.svg)](https://repology.org/project/calcurse/versions)
+
+## Building from Source
+
+Install the following build dependencies. If your distribution segments
+development files from core packages (i.e., \*-devel or \*-dev packages), you
+may need to install those as well:
 
 * gcc
 * autoconf-archive
@@ -31,8 +35,7 @@ and install calcurse:
 Note that `make install` needs to be run as root. When working on a Git
 checkout, you need to run `./autogen.sh` before `./configure`.
 
-Package Overview
-----------------
+## Source Overview
 
 * `build-aux`: auxiliary files for the build process
 * `contrib`: useful tools such as hooks or the CalDAV synchronization script
@@ -42,8 +45,7 @@ Package Overview
 * `src`: the actual calcurse source files
 * `test`: test suite and test cases for calcurse
 
-Authors
--------
+## Authors
 
 calcurse was created by Frederic Culot in 2004. Since 2011, the project is
 maintained by Lukas Fleischer. Many core features added to calcurse since 2017
@@ -53,8 +55,7 @@ Of course, there are numerous other contributors. Check the Git commit log and
 the `Thanks` section in the manual for a list of people who have contributed by
 reporting bugs, sending fixes, or suggesting improvements.
 
-Contributing and Donations
---------------------------
+## Contributing and Donations
 
 Patches, bug reports and other requests are always welcome! You can submit them
 to one of our mailing lists (check the [patch submission