Saying Hello! using a sample repository. Thanks to https://guides.github.com/activities/hello-world/ which provides us an easy way to create and maintain repositories on Github.

Alternatively, for H1 and H2, an underline-ish style:

Emphasis, aka italics, with asterisks or underscores.

Strong emphasis, aka bold, with double asterisks or double underscores.

Combined emphasis with asterisks and underscores.

Strikethrough uses two tildes. Scratch this.

1. First ordered list item
2. Another item ⋅⋅* Unordered sub-list.
3. Actual numbers don't matter, just that it's a number ⋅⋅1. Ordered sub-list
4. And another item.

• Unordered list can use asterisks

• Or minuses

• Or pluses

I'm an inline-style link

I'm an inline-style link with title

I'm a reference-style link

I'm a relative reference to a repository file

You can use numbers for reference-style link definitions

Or leave it empty and use the link text itself.

URLs and URLs in angle brackets will automatically get turned into links. http://www.example.com or http://www.example.com and sometimes example.com (but not on Github, for example).

Some text to show that the reference links can follow later.

Inline code has back-ticks around it.

var s = "JavaScript syntax highlighting";
alert(s);

s = "Python syntax highlighting"
print s

No language indicated, so no syntax highlighting. 
But let's throw in a <b>tag</b>.