Fix: Link to composer website

[localheinz]

This PR

• links to the composer website in README.md

[codecov]

Codecov Report

Merging #228 into 1.x will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##                1.x     #228   +/-   ##
=========================================
  Coverage     78.97%   78.97%           
  Complexity       41       41           
=========================================
  Files             3        3           
  Lines           195      195           
=========================================
  Hits            154      154           
  Misses           41       41

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update c406aa0...32d8701. Read the comment docs.