Update README to include Codecov link

Added link to Codecov for test coverage information.

Author: sebastian-ederer

README.md

@@ -152,6 +152,8 @@ docker-compose down -v
 
 This project uses a two-tier testing strategy to ensure code quality and correctness.
 
+> Checkout the test coverage on [Codecov](https://app.codecov.io/gh/cmdscale/CmdScale.EntityFrameworkCore.TimescaleDB)
+
 ### Test Projects
 
 | Project | Purpose |
@@ -347,4 +349,4 @@ AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 SOFTWARE.
-```
+```