README.md: add the _Table of contents_, update it with `md_toc --in-place --skip-lines 1 commonmarker README.md`

README.md

@@ -1,5 +1,25 @@
 # svg2ild
 
+## Table of contents
+
+<!--
+ Generate with: `md_toc --in-place --skip-lines 1 commonmarker README.md` (package `python3-md-toc` required).
+ Also, in GitLab, it can be replaced with just `[[_TOC_]]`.
+-->
+<!--TOC-->
+
+- [Table of contents](#table-of-contents)
+- [About](#about)
+- [Installation](#installation)
+- [How to](#how-to)
+  - [How to detect an internal format of .ild file](#how-to-detect-an-internal-format-of-ild-file)
+- [Links](#links)
+- [License](#license)
+
+<!--TOC-->
+
+## About
+
 Converts a series of `.svg` files to `.ild` animation for laser shows.
 Supports both static and animated images.
 
@@ -10,6 +30,8 @@ Description of the format:
 * Official: <https://ilda.com/resources/StandardsDocs/ILDA_IDTF14_rev011.pdf> (80 KiB, revision 011, <time>2014-11-16</time>).
 * Made by author of the `LaserBoy`: <https://laserboy.org/ilda_file_format.html>.
 
+## Installation
+
 ## How to
 
 ### How to detect an internal format of .ild file