[spp] [PATCH 2/2] docs: add desc to build docs on Ubuntu 18.04

[ogawa.yasufumi@lab.ntt.co.jp]

From: Yasufumi Ogawa <ogawa.yasufumi@lab.ntt.co.jp>

Instruction for building documentation is only for Ubuntu 16.04 LTS and
it is not considered for 18.04. It is required to install `latexmk` if
you use 18.04, and this update is to add the instruction.

Signed-off-by: Yasufumi Ogawa <ogawa.yasufumi@lab.ntt.co.jp>
---
 docs/guides/setup/getting_started.rst | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/docs/guides/setup/getting_started.rst b/docs/guides/setup/getting_started.rst
index 9847903..8cda22b 100644
--- a/docs/guides/setup/getting_started.rst
+++ b/docs/guides/setup/getting_started.rst
@@ -387,6 +387,13 @@ For PDF, inkscape and latex packages are required.
     $ sudo apt install texlive-latex-extra
     $ sudo apt install texlive-latex-recommended
 
+You might also need to install ``latexmk`` in addition to if you use
+Ubuntu 18.04 LTS.
+
+.. code-block:: console
+
+    $ sudo apt install latexmk
+
 HTML documentation is compiled by running make with ``doc-html``. This
 command launch sphinx for compiling HTML documents.
 Compiled HTML files are created in ``docs/guides/_build/html/`` and
-- 
2.17.1