Small grammar fix

Consistent punctuation with "etc." (end of line 56)

Author: GingerTrain

README.md

@@ -53,7 +53,7 @@ The TSDoc specification aims to meet these requirements:
 - **Markdown integration**: Doc comments may incorporate [CommonMark](http://commonmark.org) notations for rich text elements such as boldface, code fences, headings, tables, etc.  (This turned out to be the toughest requirement, since the Markdown grammar is very irregular and very dependent on context.) TSDoc makes special accommodations for entrenched pipelines (e.g. GitHub Pages) that expect to bring their own Markdown renderer to the party.
 - **Common core**: Common  tags such as `@param` and `@returns` will have consistent behavior across all tools.
 - **Extensible**: Each tool can supplement the core tags with custom tags for specialized scenarios.
-- **Interoperable**: The TSDoc standard guarantees that unsupported custom tags won't interfere with parsing of other content. TSDoc also eliminates Markdown ambiguities.  (Are backticks allowed inside a `{@link}` tag?  What happens if there is only one backtick? etc)
+- **Interoperable**: The TSDoc standard guarantees that unsupported custom tags won't interfere with parsing of other content. TSDoc also eliminates Markdown ambiguities.  (Are backticks allowed inside a `{@link}` tag?  What happens if there is only one backtick? etc.)
 - **Multi-package support**:  Many teams ship a collection of NPM packages that work together and are documented as a set.  The cross-referencing syntax (e.g. `{@link}` or `{@inheritdoc}`) needs a portable way to reference API items imported from other packages.  We also define  *package.json* metadata that enables tooling to detect whether a dependency's *.d.ts doc comments should be parsed as TSDoc or not.
 - **Open standard**: TSDoc is an open source, community-driven standard.  You are encouraged to contribute your own ideas and pull requests.