Add description from the ISA Manual https://github.com/riscv/riscv-isa-manual/blob/9799e5b43fa6780e58ec440774b0194debbca52b/src/zfinx.adoc?plain=1#L105

Author: root

arch/ext/Zhinx.yaml

@@ -0,0 +1,22 @@
+# yaml-language-server: $schema=../../schemas/ext_schema.json
+
+$schema: "ext_schema.json#"
+kind: extension
+name: Zhinx
+long_name: Half-precision floating-point instructions using integer registers
+description: |
+  The Zhinx extension provides half-precision floating-point instructions analogous
+  to those in the Zfh extension, except that these instructions use the integer
+  register file rather than the floating-point register file. Specifically, Zhinx
+  adds all the Zfh-extension instructions except the transfer instructions
+  (FLH, FSH, FMV.H.X, and FMV.X.H). The semantics of each Zhinx instruction are
+  identical to the corresponding Zfh instruction, except that occurrences of
+  `f` registers in the original Zfh instructions are replaced by the corresponding
+  `x` registers in Zhinx.
+
+  The Zhinx extension depends upon the Zfinx extension.
+type: unprivileged
+versions:
+  - version: "1.0.0"
+    state: ratified
+    ratification_date: 2021-11