[opam] Improves readability of opam messages after installation.

opam

@@ -142,18 +142,18 @@ depopts: [
 ]
 
 post-messages: [
-  "****** Frama-C/WP **************************************"
-  "This plug-in requires one or more external prover(s)."
-  "Recommended provers are:"
-  "- Alt-Ergo (https://alt-ergo.ocamlpro.com)"
-  "- CVC4     (https://cvc4.github.io)"
-  "- Z3       (https://github.com/Z3Prover/z3)"
-  "Use 'why3 config detect' to configure new provers."
-  "****** Ivette (new Frama-C GUI) ************************"
-  "Run 'ivette' once (online) to finalize installation."
-  "Once finalized, 'ivette' will work offline."
-  "Finalization also requires Node v16 and Yarn:"
-  "- install NVM (https://github.com/nvm-sh/nvm)"
-  "- run 'nvm use 16'"
-  "- run 'npm install --global yarn'"
+"The Frama-C/WP plug-in requires one or more external prover(s).
+Recommended provers are:
+- Alt-Ergo (https://alt-ergo.ocamlpro.com)
+- CVC4     (https://cvc4.github.io)
+- Z3       (https://github.com/Z3Prover/z3)
+Use 'why3 config detect' to configure new provers.
+ "
+"Ivette is a new GUI for Frama-C, currently in development.
+Run 'ivette' once (online) to finalize installation.
+Once finalized, 'ivette' will work offline.
+Finalization also requires Node v16 and Yarn:
+- install NVM (https://github.com/nvm-sh/nvm)
+- run 'nvm use 16'
+- run 'npm install --global yarn'"
 ]