Add readmes to the two new crates

Author: gnzlbg

crates/libm-analyze/README.md

@@ -0,0 +1,22 @@
+# libm-analyze
+
+This crate provides a single macro, `for_each_api`:
+
+```rust
+macro_rules! nop {
+    (
+        id: $id:ident;
+        arg_tys: $($arg_tys:ty),*;
+        arg_ids: $($arg_ids:ident),*;
+        ret: $ty:ty;
+    ) => {};
+}
+
+libm_analyze::for_each_api!(nop);
+```
+
+This macro takes a user-provided macro, and expands it for all libm APIs.
+
+For example, see how the `libm-test` crate `tests/system.rs` test uses it to
+test all `libm` APIs against random inputs, and verify the results against the
+system's libm library.

crates/libm-test/README.md

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+# libm-test
+
+This crate contains different types of test for the `libm` crate.
+
+* `tests/system.rs`: generate random inputs, and tests that the results of the
+  `libm` crate are within the tolerance required by the IEEE from those of the
+  system's libm library (e.g. musl, glibc's libm, libSystem_m, etc.).
+  
+* `tests/unit.rs`: contains some small unit tests.