diff --git a/README.md b/README.md
index 945fde3..2ab3281 100644
--- a/README.md
+++ b/README.md
@@ -13,9 +13,17 @@ If you're doing developement remember: better-test *cannot* run on itself.
 To view the arguments for Better Test run `raco better-test -h`.
 
 Code coverage can be generated by specifying the `-c <format>` flag.
-Right now the valid formats are: html and coveralls.
+Right now the valid formats are: `html` and `coveralls`.
+
+`html` simply generates html files for each source file containing coverage information and
+highlighted source code. 
+
+`coveralls` generates a coveralls coverage report and sends it to coveralls.
 Using coveralls requires the "COVERALLS_REPO_TOKEN" to be set, and needs bash and curl.
 Travic-ci/Coveralls support coming soon...
+
+Note that coveralls expect coverage by line. To convert from an expression based coverage to line based coverage we consider any line with any unrun expression to be not run.
+
 The directory that the coverage is outputted to can be specified with the `-d` flag.
 
 If any tests run by `rackunit` fail, Better Test will return with exit code `1`. If all tests pass it will return with exit code `0`.