Mention generate-abi3-import-lib in the features guide

Update the feature list section of the user guide
to include `generate-abi3-import-lib` description.

guide/src/features.md

@@ -30,6 +30,17 @@ These features are extensions of the `abi3` feature to specify the exact minimum
 
 See the [building and distribution](building_and_distribution.md#minimum-python-version-for-abi3) section for further detail.
 
+### `generate-abi3-import-lib`
+
+This experimental feature is used to generate import libraries for the Stable ABI Python DLL
+for MinGW-w64 and MSVC (cross-)compile targets.
+
+Enabling it allows to (cross-)compile `abi3` extension modules to any Windows targets
+without having to install the Windows Python distribution files for the target.
+
+See the [building and distribution](building_and_distribution.md#building-abi3-extensions-without-a-python-interpreter)
+section for further detail.
+
 ## Features for embedding Python in Rust
 
 ### `auto-initialize`