Make examples buildable

It now excludes .tox from conf.py.
It locally clones docutils cheatsheet as examples (it should be noted
that cheatsheet.txt is renamed index.rst in it).

[1] https://docutils.sourceforge.io/docs/user/rst/cheatsheet.txt

Issue-ID: DOC-772

Signed-off-by: Cédric Ollivier <cedric.ollivier@orange.com>
Change-Id: Ifd616b797d5a48da5df77b0dfaa0613497b742d8
diff --git a/examples/sphinx/istanbul/tox.ini b/examples/sphinx/istanbul/tox.ini
new file mode 100644
index 0000000..8b5bc99
--- /dev/null
+++ b/examples/sphinx/istanbul/tox.ini
@@ -0,0 +1,25 @@
+[tox]
+minversion = 1.6
+envlist = docs,docs-linkcheck
+skipsdist = true
+
+[testenv:docs]
+basepython = python3
+deps =
+    -r{toxinidir}/requirements-docs.txt
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.os.txt?h=istanbul
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.onap.txt?h=istanbul
+commands =
+    sphinx-build -W -b html -n -d {envtmpdir}/doctrees ./ {toxinidir}/_build/html
+    echo "Generated docs available in {toxinidir}/_build/html"
+whitelist_externals =
+    echo
+
+[testenv:docs-linkcheck]
+basepython = python3
+deps =
+    -r{toxinidir}/requirements-docs.txt
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.os.txt?h=istanbul
+    -chttps://git.onap.org/doc/plain/etc/upper-constraints.onap.txt?h=istanbul
+commands =
+    sphinx-build -W -b linkcheck -d {envtmpdir}/doctrees ./ {toxinidir}/_build/linkcheck