Update the notes for developers

Author: joto

NOTES_FOR_DEVELOPERS.md

@@ -136,15 +136,8 @@ directory, some data tests in `test/osm-testdata` and tests of the examples in
 `test/examples`. They are built by the default cmake config. Run `ctest` to
 run them. We can always use more tests.
 
-Tests are run automatically using the Travis (Linux/Mac) and Appveyor (Windows)
-services. We automatically create coverage reports on Codevoc.io. Note that
-the coverage percentages reported are not always accurate, because code that
-is not used in tests at all will not necessarily end up in the binary and
-the code coverage tool will not know it is there.
-
-[![Travis Build Status](https://secure.travis-ci.org/osmcode/libosmium.svg)](https://travis-ci.org/osmcode/libosmium)
-[![Appveyor Build Status](https://ci.appveyor.com/api/projects/status/github/osmcode/libosmium?svg=true)](https://ci.appveyor.com/project/Mapbox/libosmium)
-[![Coverage Status](https://codecov.io/gh/osmcode/libosmium/branch/master/graph/badge.svg)](https://codecov.io/gh/osmcode/libosmium)
+Tests are run automatically using Github Actions (Linux/macOS) and Appveyor
+(Windows) services.
 
 
 ## Documenting the code