docs: improve links back to GitHub (#1181)

This fixes the view button, adds an edit button (not that fond of it,
but since there's also a view, I think it's fine), and adds a little
github logo at the bottom. I'd rather it at the top, but this is where
it's natural in this theme.

Signed-off-by: Henry Schreiner <henryfs@princeton.edu>

Author: henryiii

docs/conf.py

@@ -126,6 +126,26 @@
 #
 html_theme = "furo"
 
+html_theme_options = {
+    "source_repository": "https://github.com/scikit-build/scikit-build-core",
+    "source_branch": "main",
+    "source_directory": "docs/",
+    "footer_icons": [
+        {
+            "name": "GitHub",
+            "url": "https://github.com/scikit-build/scikit-build-core",
+            "html": """
+                <svg stroke="currentColor" fill="currentColor" stroke-width="0" viewBox="0 0 16 16">
+                    <path fill-rule="evenodd" d="M8 0C3.58 0 0 3.58 0 8c0 3.54 2.29 6.53 5.47 7.59.4.07.55-.17.55-.38 0-.19-.01-.82-.01-1.49-2.01.37-2.53-.49-2.69-.94-.09-.23-.48-.94-.82-1.13-.28-.15-.68-.52-.01-.53.63-.01 1.08.58 1.23.82.72 1.21 1.87.87 2.33.66.07-.52.28-.87.51-1.07-1.78-.2-3.64-.89-3.64-3.95 0-.87.31-1.59.82-2.15-.08-.2-.36-1.02.08-2.12 0 0 .67-.21 2.2.82.64-.18 1.32-.27 2-.27.68 0 1.36.09 2 .27 1.53-1.04 2.2-.82 2.2-.82.44 1.1.16 1.92.08 2.12.51.56.82 1.27.82 2.15 0 3.07-1.87 3.75-3.65 3.95.29.25.54.73.54 1.48 0 1.07-.01 1.93-.01 2.2 0 .21.15.46.55.38A8.013 8.013 0 0 0 16 8c0-4.42-3.58-8-8-8z"></path>
+                </svg>
+            """,
+            "class": "",
+        },
+    ],
+}
+html_copy_source = False
+html_show_sourcelink = False
+
 
 # -- Extension configuration -------------------------------------------------
 myst_enable_extensions = [