drone: add drone config

This add support for cloud.drone.io CI on master/edge

Supported arches are

- x86
- x86_64
- armhf
- armv7
- aarch64

.drone.yml

+---
+kind: pipeline
+name: edge-x86
+
+clone:
+  depth: 50
+
+platform:
+  os: linux
+  arch: amd64
+
+workspace:
+  base: /home/buildozer/drone
+  path: aports
+
+steps:
+  - name: build
+    image: alpinelinux/alpine-drone-ci:edge-x86
+    commands:
+      - build.sh
+    environment:
+      GH_TOKEN:
+        from_secret: github_token
+    pull: always
+
+trigger:
+  event:
+    - pull_request
+
+---
+kind: pipeline
+name: edge-x86_64
+
+clone:
+  depth: 50
+
+platform:
+  os: linux
+  arch: amd64
+
+workspace:
+  base: /home/buildozer/drone
+  path: aports
+
+steps:
+  - name: build
+    image: alpinelinux/alpine-drone-ci:edge-x86_64
+    commands:
+      - build.sh
+    environment:
+      GH_TOKEN:
+        from_secret: github_token
+    pull: always
+
+trigger:
+  event:
+    - pull_request
+
+---
+kind: pipeline
+name: edge-aarch64
+
+clone:
+  depth: 50
+
+platform:
+  os: linux
+  arch: arm64
+
+workspace:
+  base: /home/buildozer/drone
+  path: aports
+
+steps:
+  - name: build
+    image: alpinelinux/alpine-drone-ci:edge-aarch64
+    commands:
+      - build.sh
+    environment:
+      GH_TOKEN:
+        from_secret: github_token
+    pull: always
+
+trigger:
+  event:
+    - pull_request
+
+---
+kind: pipeline
+name: edge-armhf
+
+clone:
+  depth: 50
+
+platform:
+  os: linux
+  arch: arm
+
+workspace:
+  base: /home/buildozer/drone
+  path: aports
+
+steps:
+  - name: build
+    image: alpinelinux/alpine-drone-ci:edge-armhf
+    commands:
+      - build.sh
+    environment:
+      GH_TOKEN:
+        from_secret: github_token
+    pull: always
+
+trigger:
+  event:
+    - pull_request
+
+---
+kind: pipeline
+name: edge-armv7
+
+clone:
+  depth: 50
+
+platform:
+  os: linux
+  arch: arm
+
+workspace:
+  base: /home/buildozer/drone
+  path: aports
+
+steps:
+  - name: build
+    image: alpinelinux/alpine-drone-ci:edge-armv7
+    commands:
+      - build.sh
+    environment:
+      GH_TOKEN:
+        from_secret: github_token
+    pull: always
+
+trigger:
+  event:
+    - pull_request
+