Add code coverage instructions to README.md

README.md

@@ -144,6 +144,22 @@ Mosh has a Perl dependency that is only required for client use.  For
 some platforms, it may make sense to have separate mosh-server and
 mosh-client packages to allow mosh-server usage without Perl.
 
+Notes for developers
+--------------------
+
+Mosh supports producing code coverage reports by tests, but this feature is
+disabled by default. To enable it, make sure `lcov` is installed on your
+system. Then, configure and run tests:
+
+```
+$ ./configure --enable-code-coverage
+$ make check-code-coverage
+```
+
+This will run all tests and produce a coverage report in HTML form that can be
+opened with your favorite browser. Ideally, newly added code should strive for
+90% (or better) incremental test coverage.
+
 More info
 ---------