[doc] Use consistent spelling/capitalization of names

Consistently use the following spelling for document formats,
programming languages, and names:

- Markdown
- Hjson
- JSON
- Verilog
- HTML
- GitHub
- CSS
- Python

Also avoid abbreviations:
- repo -> repository

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/doc/ug/quickstart.md b/doc/ug/quickstart.md
index fa84544..69d8c81 100644
--- a/doc/ug/quickstart.md
+++ b/doc/ug/quickstart.md
@@ -20,7 +20,7 @@
 
 ## Extract the release
 
-Download a release bitstream from the [OpenTitan Github Releases page](https://github.com/lowRISC/opentitan/releases) and extract it.
+Download a release bitstream from the [OpenTitan GitHub Releases page](https://github.com/lowRISC/opentitan/releases) and extract it.
 `$OT_TOP` refers to the location where it is extracted.
 
 ```console