docs:

  add README files to describe folder contents and usage

Author: thomasleplus

src/README.md

@@ -0,0 +1,12 @@
+# Source
+
+Maven sources for `java-sql-inspector`, which parses SQL and inspects it.
+
+- `main/antlr4/org/leplus/antlr4/PLSQL.g4` — the ANTLR4 PL/SQL grammar; the
+  antlr4 Maven plugin generates the parser from it at build time.
+- `main/java/org/leplus/sql/` — the inspector: `Inspector` drives parsing,
+  `ConstantListener` walks the parse tree, `Result` holds findings, and
+  `ExceptionErrorListener` turns parse errors into exceptions.
+- `test/java/org/leplus/sql/` — JUnit tests and assertions.
+
+Build/test with `./mvnw test` (grammar is compiled automatically).