[docs] Added a stub page for the writers to edit (#1518)

<!--- Provide a general summary of your changes in the Title above -->

## Motivation and Context

It's just a stub page for the writers to start working on their own
section on our website.
The page will be available by this url:
https://developer.semrush.com/intergalactic/content/punctuation/punctuation

## Types of changes

<!--- What types of changes does your code introduce? Put an `x` in all
the boxes that apply: -->

- [ ] Bug fix (non-breaking change which fixes an issue).
- [ ] New feature (non-breaking change which adds functionality).
- [ ] Breaking change (fix or feature that would cause existing
functionality to not work as expected).
- [x] Nice improve.

## Checklist:

<!--- Go over all the following points, and put an `x` in all the boxes
that apply. -->
<!--- If you're unsure about any of these, don't hesitate to ask. We're
here to help! -->

- [ ] My code follows the code style of this project.
- [x] I have updated the documentation accordingly or it's not required.
- [ ] Unit tests are not broken.
- [ ] I have added changelog note to corresponding `CHANGELOG.md` file
with planned publish date.
- [ ] I have added new unit tests on added of fixed functionality.

website/docs/content/punctuation/punctuation.md

@@ -0,0 +1,14 @@
+---
+title: Punctuation and special symbols
+---
+
+## Dashes and hyphens
+
+### Em dash (—)
+
+| Symbol       | HTML entity        |
+| :----------: | :----------------: |
+| —      | `—`          |
+
+* Use sparingly in sentences in place of a comma or colon
+* Omit the spaces on both sides of the dash