[doc] Consistently use title and headings

* Add a "title" attribute to make the page title show up in the
  generated TOC. (The first heading isn't used there unfortunately.)
* The title serves as "h1" heading, use "h2" headings (`##`) and below
  within the document.

Signed-off-by: Philipp Wagner <phw@lowrisc.org>
diff --git a/doc/ug/getting_started_sw.md b/doc/ug/getting_started_sw.md
index f0c2aab..dbf54e2 100644
--- a/doc/ug/getting_started_sw.md
+++ b/doc/ug/getting_started_sw.md
@@ -1,4 +1,6 @@
-# Build Software
+---
+title: Build Software
+---
 
 ## Prerequisites
 
@@ -80,4 +82,4 @@
 ```
 
 If you do not specify your own toolchain configuration file (using `./meson_init.sh -t`), and `meson_init.sh` cannot find the default configuration in your toolchain, the legacy `toolchain.txt` from the main OpenTitan repository will be used.
-If `TOOLCHAIN_PATH` is set, this will be used to update any paths within the legacy configuration.
\ No newline at end of file
+If `TOOLCHAIN_PATH` is set, this will be used to update any paths within the legacy configuration.