📝 Document matcher caveats in the README

State the end-user limits once, in README § Caveats: a member colliding
with its stringification, the unsupported symbol/bigint, and NaN/-0. Drop
the duplicated known-issue prose from development/library.md and the
source comment; link to the README instead.

src/primitive.ts

@@ -3,16 +3,13 @@ import type { Exact, ValueOf } from "type-fest";
 type UnaryFn<T, R> = (shape: T) => R;
 
 // The primitive universe a matcher can discriminate. `boolean` is admitted as
-// the pair `true | false`; `symbol` is deliberately absent (a brand is a
-// compile-time phantom, so there is nothing to match at runtime).
+// the pair `true | false`; see README § Caveats for the unsupported members.
 type Matchable = string | number | boolean | null | undefined;
 
 // `boolean`, `null` and `undefined` cannot be property keys, so a mapped type
 // over the universe keys each non-key member by its stringification. `Param`
 // inverts that projection, so a handler callback still receives the *real*
-// member (`true`, not `"true"`). A universe mixing a member with the string it
-// stringifies to (e.g. `true | "true"`) collapses to one key and is not
-// representable — see development/library.md.
+// member (`true`, not `"true"`) — see README § Caveats for the limits.
 type PatternKey<T> = T extends boolean
     ? T extends true
         ? "true"