add linting CI

.drone.yml

@@ -0,0 +1,14 @@
+---
+kind: pipeline
+type: docker
+name: lint
+
+steps:
+  - name: yaml linting
+    image: pipelinecomponents/yamllint
+    commands:
+      - yamllint .
+  - name: markdown linting
+    image: 06kellyjac/markdownlint-cli
+    commands:
+      - markdownlint . -i themes

.markdownlint.yaml

@@ -0,0 +1,9 @@
+---
+# Default state for all rules
+default: true
+MD009:
+    strict: false
+
+MD013: false
+MD033: false
+MD024: false

.yamllint

@@ -0,0 +1,9 @@
+extends: default
+
+ignore: themes/
+
+rules:
+  # 80 chars should be enough, but don't fail if a line is longer
+  line-length:
+    max: 80
+    level: warning