docs: fix tests badge

README.md

@@ -1,6 +1,6 @@
 # xstdin
 
-[![tests](https://github.com/patte/xstdin-rs/actions/workflows/test-and-lint.yml/badge.svg)]
+[![tests](https://github.com/patte/xstdin-rs/actions/workflows/test-and-lint.yml/badge.svg)](https://github.com/patte/xstdin-rs/actions/workflows/test-and-lint.yml)
 
 CLI tool for distributing stdin to a set of long-running workers.
 By default, distributes input in chunks of ~8KiB (always on line boundaries) to 4 workers.
@@ -97,4 +97,4 @@ time pv --rate input_large.txt | xstdin -- wc -l | awk '{s+=$1} END {print s}'
 pv --rate input_large.txt  0.11s user 2.46s system 44% cpu 5.828 total
 xstdin -- wc -l  11.05s user 4.86s system 272% cpu 5.827 total
 awk '{s+=$1} END {print s}'  0.00s user 0.00s system 0% cpu 5.827 total
-``````
+``````