Documentation about SignatureRegexes (#7689)

Author: mernst

checker-qual/src/main/java/org/checkerframework/checker/signature/qual/README.md

@@ -0,0 +1,7 @@
+# No `@QualifierForLiteral` annotations
+
+These type qualifiers have no `@QualifierForLiteral` annotations.  Instead, they
+use the regular expressions in
+[reflection-util](https://github.com/plume-lib/reflection-util/)'s
+[`SignatureRegexes`
+class](https://github.com/plume-lib/reflection-util/blob/master/src/main/java/org/plumelib/reflection/SignatureRegexes.java).

framework/src/main/java/org/checkerframework/framework/type/treeannotator/LiteralTreeAnnotator.java

@@ -297,6 +297,7 @@ public Void visitLiteral(LiteralTree tree, AnnotatedTypeMirror type) {
                     " the glb of `matches` for \"" + string + "\" is " + res,
                     " which is a subtype of " + sam,
                     " whose pattern does not match \"" + string + "\".",
+                    "  patterns = " + stringPatterns,
                     "  matches = " + matchesOnePerLine,
                     "  nonMatches = " + nonMatches));
           }