snippets: rtt-console: fix README issues

- Title underline too long
- Remove redundant how-to-use snippet bit, this can be documented
  generically for all snippets instead of repeating it everywhere.
- Snippet does not redirect anything.
- RTT does not require HW support for console.

Signed-off-by: Gerard Marull-Paretas <gerard@teslabs.com>

snippets/rtt-console/README.rst

@@ -1,21 +1,16 @@
 .. _snippet-rtt-console:
 
 RTT Console Snippet (rtt-console)
-#########################################
+#################################
-
-.. code-block:: console
-
-   west build -S rtt-console [...]
 
 Overview
 ********
 
-This snippet redirects serial console output to SEGGER RTT.
+This snippet enables console output to SEGGER RTT.
 
 Requirements
 ************
 
-Hardware support for:
+Support for:
 
 - :kconfig:option:`CONFIG_HAS_SEGGER_RTT`
-- :kconfig:option:`CONFIG_CONSOLE`