Feat/markdown tables (#665)

* docs(contributing): add yarn to one-time docker use

* feat(markdown): add lists and tables

- add h2 example

CONTRIBUTING.md

@@ -27,7 +27,7 @@ First time setup:
 docker-compose build
 
 # First-time setup
-docker-compose run --rm web bundle install
+docker-compose run --rm web bundle install && yarn
 ```
 
 Starting the server:

markdown.md

@@ -14,6 +14,7 @@ weight: -1
 
 ```markdown
 # h1
+## h2
 ### h3
 ```
 
@@ -43,6 +44,18 @@ __bold__
 `code`
 ```
 
+### Lists
+
+```markdown
+* Item 1
+* Item 2
+```
+
+```markdown
+- Item 1
+- Item 2
+```
+
 ### Links
 
 ```markdown
@@ -109,3 +122,17 @@ codeFences.withLanguage()
 ```markdown
 ****
 ```
+
+### Tables
+
+```markdown
+| Column 1 Heading | Column 2 Heading |
+| ---------------- | ---------------- |
+| Some content     | Other content    |
+```
+
+```markdown
+Column 1 Heading | Column 2 Heading
+--- | ---
+Some content | Other content
+```