docs) add welcome note for new developers

HELLO.md

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+Hello and welcome to the Trips repository!
+
+We are glad you are here. This project uses standard git workflows and follows the conventions already in the codebase.
+
+If you are just getting started, begin by reading the README and browsing the main modules to understand the structure.

HELLOWORLD.md

@@ -1,7 +0,0 @@
-Hello and welcome to the Trips project!
-
-We're glad you're here. This repository is the home for the Trips application and the tools that support it.
-
-If you're new, start with `README.md` to get the project running, then take a look around `src/` to see how things are organized.
-
-Happy building!