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

docs/LINTER.md

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+# Claro Checker
+
+`claro check file.claro` looks for beginner mistakes before running a program.
+
+RC3 catches:
+
+- unknown commands
+- command typos such as `PRINT` or `PRNT`
+- missing `TO` in `SET`
+- missing `AS` in `ASK`, `GET`, and `COUNT`
+- missing `ENDIF`, `DONE`, `LEARNED`, `ENDTRY`, and other block endings
+- `ELSE` without an `IF`
+- `CATCH` without a `TRY`
+- common misspelled variables
+- variables created by `ASK`, `GET`, `COUNT`, `READ`, `PARSE`, `MAKE`, `FOR`, and `FOR EACH`
+
+The checker is meant to be friendly, not scary. It is still not a complete static analyzer.