documentation: Fix evaluation of reStructuredText

eval_rst isn't a valid directive. Use eval-rst instead. Also, add curly
braces where necessary since the MyST parser requires them.

Change-Id: I68337354e9bd4de4b2c29d4e42c3bb22337fbe06
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83117
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Nicholas Chin <nic.c3.14@gmail.com>

Documentation/getting_started/writing_documentation.md

@@ -99,7 +99,7 @@ To reference documents use the TOC tree or inline RST code.
 Under Sphinx markdown tables are not supported. Therefore you can use following
 code block to write tables in reStructuredText and embed them into the markdown:
 
-    ```eval_rst
+    ```{eval-rst}
     +------------+------------+-----------+
     | Header 1   | Header 2   | Header 3  |
     +============+============+===========+
@@ -144,7 +144,7 @@ you'll see the following warning:
 You can import CSV files and let sphinx automatically convert them to human
 readable tables, using the following reStructuredText snipped:
 
-    ```eval_rst
+    ```{eval-rst}
     .. csv-table::
        :header: "Key", "Value"
        :file: keyvalues.csv