Add a table with tested formats

Author: fjarri

serdect/README.md

@@ -29,6 +29,18 @@ While this crate can't ensure that format implementations don't perform
 other kinds of data-dependent branching on the contents of the serialized data,
 using a constant-time hex serialization with human-readable formats should
 help reduce the overall timing variability.
+The table below lists the crates `serdect` is tested against.
+❌ marks the cases for which the serialization is not constant-size for a given data size (due to the format limitations), and therefore will not be constant-time too.
+
+| Crate                                                              | `array`  | `slice`  |
+|--------------------------------------------------------------------|:--------:|:--------:|
+| [`bincode`](https://crates.io/crates/bincode) v1                   | ✅ | ✅ |
+| [`ciborium`](https://crates.io/crates/ciborium) v0.2               | ❌ | ✅ |
+| [`rmp-serde`](https://crates.io/crates/rmp-serde) v1               | ❌ | ✅ |
+| [`serde-json-core`](https://crates.io/crates/serde-json-core) v0.5 | ✅ | ✅ |
+| [`serde-json`](https://crates.io/crates/serde-json) v1             | ✅ | ✅ |
+| [`toml`](https://crates.io/crates/toml) v0.7                       | ✅ | ✅ |
+
 
 ## Minimum Supported Rust Version