docs: add SPEC.md, the first written specification of zc

Reference for lexing, types, expressions (full precedence table),
statements, declarations, the ownership analyzer and its messages,
compile-time execution and the runtime contract, with appendices for
the zc0 subset and for doc/implementation disagreements and bugs found
while checking the rules against build/bin/zy. Pointers added to
README.md and ONBOARD.md.

1 files changed, 1 insertions, 1 deletions

diff --git a/ONBOARD.md b/ONBOARD.md
index a0ed367..6fa9c0e 100644
--- a/ONBOARD.md
+++ b/ONBOARD.md
@@ -60,7 +60,7 @@ for f in examples/learn/*.zc; do echo "== $f"; build/bin/zy < $f; done
 python3 tests/drivers/learn.py build/bin/zy
 ```
 
-then read the language parts of `README.md`: "zc, the language", "memory model",
+keep `docs/SPEC.md`, the language reference, open beside it for the exact rules (precedence, types, ownership errors); then read the language parts of `README.md`: "zc, the language", "memory model",
 "types", "o3", "code as data". run a few of the larger examples
 (`examples/lang.zc`, `examples/bf.zc`, `examples/dump.zc`, `examples/tree.zc`).