Clarify some descriptions

Change-Id: I3177c468eeec3f1de49d6e2d71889c36acf202bc
diff --git a/mbed-tls-nightly-tests.yaml b/mbed-tls-nightly-tests.yaml
index 17a362e..f2eee8a 100644
--- a/mbed-tls-nightly-tests.yaml
+++ b/mbed-tls-nightly-tests.yaml
@@ -6,20 +6,17 @@
     parameters:
     - string:
         default: ssh://git@github.com/Mbed-TLS/mbedtls.git
-        description: Enter mbed TLS repo/fork
+        description: Mbed TLS repo/fork
         name: MBED_TLS_REPO
         trim: 'false'
     - string:
         default: development
-        description: Enter branch or commit to test
+        description: Branch or commit to test
         name: MBED_TLS_BRANCH
         trim: 'false'
     - bool:
         default: true
-        description: |-
-          Run basic-build-test.sh
-
-          (Note, this does not work on mbedtls-2.1).
+        description: Run basic-build-test.sh (test coverage measurement)
         name: RUN_BASIC_BUILD_TEST
     - bool:
         default: true