Add docs/RC3_NOTES.md from Claro v1.17.26 zip

docs/RC3_NOTES.md

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+# Claro RC3 Notes
+
+Claro RC3 is the **Classroom Readiness Release**.
+
+RC3 does not try to make Claro bigger. It makes the existing beginner language easier to teach, test, and package.
+
+## New in RC3
+
+- Version now reports `Claro RC3`.
+- Added a `lessons/` folder with a first-hour learning path.
+- Added `build.bat` and `run_tests.bat` for Windows users who do not want to use PowerShell scripts.
+- Updated `build.ps1` for RC3.
+- Improved `claro check` diagnostics:
+  - better command typo suggestions, such as `PRNT` -> `SAY`
+  - missing block messages point back to the line where the block started
+  - `ELSE` without `IF` and `CATCH` without `TRY` are reported
+  - `TEACH` parameters are understood by the checker
+  - `FOR` loop variables and `FOR EACH` variables are understood by the checker
+  - `GET`, `COUNT`, `ASK`, file/JSON commands with `AS` are tracked as variables
+- Added more beginner example programs.
+- Added `tools/validate_rc3.py` for release validation.
+
+## RC3 focus
+
+RC3 is meant for learners, teachers, parents, and testers to try Claro without running into avoidable setup and beginner-error problems.
+
+## Still not final 1.0
+
+- SDL graphics remain experimental only.
+- No package manager yet.
+- No IDE extension yet.
+- The checker is helpful but not a complete static analyzer.