[CI] Add som linters (yaml, docker and markdown)

.drone.yml

@@ -1,3 +1,23 @@
+---
+kind: pipeline
+name: lint
+
+steps:
+- name: yaml lint
+  image: cytopia/yamllint
+  commands:
+  - yamllint .
+
+- name: docker lint
+  image: hadolint/hadolint
+  commands:
+  - hadolint Dockerfile  # ignore pinning version in pip
+
+- name: markdown lint
+  image: pipelinecomponents/markdownlint:latest
+  commands:
+  - mdl --style all --warnings .
+
 ---
 kind: pipeline
 name: build
@@ -16,6 +36,8 @@ steps:
     event:
       exclude:
       - pull_request
+depends_on:
+- lint
 
 ---
 deploy_commands_alias:

.yamllint

@@ -0,0 +1,9 @@
+---
+extends: default
+
+rules:
+  indentation:
+    indent-sequences: consistent
+  line-length:
+    max: 170
+    level: warning