add labeler (#5078)

.github/label.yml

@@ -0,0 +1,12 @@
+name: labeler
+on: [pull_request_target]
+
+permissions:
+  contents: read
+  pull-requests: write
+
+jobs:
+  label:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/labeler@v4

.github/labeler.yml

@@ -0,0 +1,26 @@
+cmake:
+- cmake/**
+- **/CMakeLists.txt
+- **/*.cmake
+- toolchains/**
+
+doc: docs/**
+
+python: python/**
+
+example: examples/**
+
+test: tests/**
+
+tool: tools/**
+pnnx: tools/pnnx/**
+
+core: src/*
+layer: src/layer/*
+
+arm: src/layer/arm/**
+loongarch: src/layer/loongarch/**
+mips: src/layer/mips/**
+riscv: src/layer/riscv/**
+vulkan: src/layer/vulkan/**
+x86: src/layer/x86/**