docs: Add documentation on pkgconfig.relocatable

- Documentation for the pkgconfig.relocatable module option in
Builtin-options. Gives an explanation on what it does, usefulness and
what error that can occur when using it.

- Add pkgconfig.relocatable release snippet. Similar to the
documentation in Builtin-options. Just a bit more brief.

- Add Pkgconfig to DataTests.test_builtin_options_documented in the
docs unit tests.

1 files changed, 1 insertions, 1 deletions

diff --git a/unittests/datatests.py b/unittests/datatests.py
index 4d4d3a19e..9a46ec475 100644
--- a/unittests/datatests.py
+++ b/unittests/datatests.py
@@ -128,7 +128,7 @@ class DataTests(unittest.TestCase):
         mod_subcontents = []
         content = self._get_section_content("Module options", sections, md)
         subsections = tee(re.finditer(r"^### (.+)$", content, re.MULTILINE))
-        for idx, mod in enumerate(['Python']):
+        for idx, mod in enumerate(['Pkgconfig', 'Python']):
             mod_subcontents.append(self._get_section_content(f'{mod} module', subsections[idx], content))
         for subcontent in u_subcontents + mod_subcontents:
             # Find the option names