[README] Update the tag descriptions.

README.md

@@ -5,3 +5,24 @@
 * Test data is from [WebAssembly Core Tests](https://github.com/WebAssembly/spec/tree/master/test/core).
 
 * [S-Expression script](https://github.com/WebAssembly/spec/blob/master/interpreter/README.md#s-expression-syntax) of tests are extracted into `json` and `wasm` files by [wast2json](https://webassembly.github.io/wabt/doc/wast2json.1.html) tool in [wabt](https://github.com/WebAssembly/wabt).
+
+# Branches and Tags
+
+## Active Branches
+
+* `master`: The newest test suite from the [WebAssembly Spec](https://github.com/WebAssembly/spec/).
+* `wasm-dev`: The developing branch for the newest [SSVM](https://github.com/second-state/SSVM).
+
+## Newest Tags
+
+* `wasm-core-20210414`: The test suite in the date 2021/04/14 from the WASM spec.
+
+## Inactive Branches
+
+* `wasm-core`: The older test suite for the [SSVM 0.7.2](https://github.com/second-state/SSVM/releases/tag/0.7.2) and [SSVM 0.7.3](https://github.com/second-state/SSVM/releases/tag/0.7.3). Deprecated and will not update.
+
+## Older Tags
+
+* `wasm-ref-types`: The test suite for the bulk-memory-operations and reference-types proposals.
+* `wasm-1.1`: The test suite for the WASM 1.1.
+* `wasm-1.0`: The test suite for the WASM 1.0.