Add docs about coverage reports (#5958)

* Add docs about running coverage tests locally

* Add link to CI coverage report

* higlight that we only cover unit tests

* Add CI coverage report image

* Add more steps

* Remove OOM instructions

docs/DEVELOPMENT.md

@@ -153,6 +153,28 @@ Use [pprof](https://github.com/google/pprof) and the following command to genera
 
 ![call-graph example](./imgs/call-graph-profile.png)
 
+### Coverage reports
+
+We generate coverage reports every day that can be accessed [here](https://app.codecov.io/gh/qdrant/qdrant/tree/code-coverage)
+
+Note: These reports **only cover the Rust unit tests** (for now)
+
+![CI coverage report](./imgs/ci-coverage-report.png)
+
+You can also generate coverage reports locally with the following commands
+
+```bash
+cd qdrant
+cargo install cargo-llvm-cov
+./tools/coverage.sh
+
+cd target/llvm-cov/html
+python -m http.server
+open http://localhost:8000
+```
+
+![Local coverage report](./imgs/local-coverage-report.png)
+
 ### Tango.rs-based benchmarks
 
 Some benchmarks are implemented using the [Tango.rs](https://github.com/bazhenov/tango) framework.