Merge #3352

3352: Add benchmarking section to README r=heinrich5991 a=def-

<!-- What is the motivation for the changes of this pull request -->

## Checklist

- [ ] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test if it works standalone, system.c especially
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: def <dennis@felsin9.de>

README.md

@@ -192,7 +192,7 @@ $ ./DDNet-Server -f mine.cfg
 </a>
 
 Installation from Repository
------------------
+----------------------------
 
 Debian/Ubuntu
 
@@ -219,4 +219,11 @@ Arch Linux
 $ yay -S ddnet
 ```
 
+Benchmarking
+------------
 
+DDNet is available in the [Phoronix Test Suite](https://openbenchmarking.org/test/pts/ddnet). If you have PTS installed you can easily benchmark DDNet on your own system like this:
+
+```bash
+$ phoronix-test-suite benchmark ddnet
+```