ci/images/README: clarify usage of build.sh for Coverity Scan

diff --git a/ci/images/README.md b/ci/images/README.md
index 531c70c58d9e2979e6ff7398ff3256a1e3af32f6..0224960d00405acf5608c4836af36daff10f8b1e 100644 (file)
--- a/ci/images/README.md
+++ b/ci/images/README.md
@@ -15,6 +15,14 @@ inputs for [Coverity Scan](https://scan.coverity.com/).
 It is used by the `coverity` CI job to generate and send data to Coverity Scan
 for analysis.
 
+To build this image, you need to retrieve the Coverity Scan token from the
+dashboard and pass it to the `build.sh` script using the `COVERITY_SCAN_TOKEN`
+environment variable, e.g.:
+
+```
+$ COVERITY_SCAN_TOKEN=the_secret_token ./build.sh debian-11-coverity
+```
+
 ### debian-bullseye
 
 Used to serve the same purpose as `debian-11`. As of 2022-03-09, it is still