[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/directory_structure.md b/doc/ug/directory_structure.md
index 77bb24d..95e2332 100644
--- a/doc/ug/directory_structure.md
+++ b/doc/ug/directory_structure.md
@@ -2,7 +2,7 @@
 title: "Directory Structure"
 ---
 
-This document provides an overview of the opentitan repo directory structure.
+This document provides an overview of the opentitan repository directory structure.
 The hierarchy underneath the root is fairly self explanatory, containing the following:
 * `doc`: High level documentatation, user guides and reference manuals
 * `util`: Helper scripts and generator tools