Add note about msys2 CI runs to README

Author: sio

README.md

@@ -30,11 +30,12 @@ To enable the described behavior source [**this file**][main] from your
 
 Completion functions have been tested and reported to work on:
 
-- Linux (Debian 9,10)
+- Linux (Debian 9, 10, 11)
 - macOS (requires gnu-sed from brew)
-- Windows (MSYS)
+- Windows (msys2, Git for Windows)
 
-[Automated tests](tests/README.md) are performed on Linux, FreeBSD and macOS.
+[Automated tests](tests/README.md) are continuously executed
+on Linux, FreeBSD, macOS and Windows (msys2).
 
 
 ## Installation and updating

tests/README.md

@@ -59,6 +59,10 @@ Automated tests are continuously executed after each push to this repo.
 - **FreeBSD** tests are executed in Google Cloud Platfom [VM images] on
   infrastructure provided by [Cirrus CI]:
     - FreeBSD 12.2: bash 5.1, sed 4.8 *(automatically updated in each CI run)*
+- **Windows** is not a native platform for bash, and there are several
+  compatibility layers people use to work around that (msys2, cygwin, WSL).
+  Currently continuous integration tests are executed only on **msys2**
+  provided by [GitHub Actions].
 
 [GitHub Actions]: https://github.com/features/actions
 [Docker containers]: docker/README.md