Move the comment about Sphinx 1.4 out of the top-level README.

cranelift/README.md

@@ -132,6 +132,3 @@ generator](https://www.sphinx-doc.org/):
     $ cd cranelift/docs
     $ make html
     $ open _build/html/index.html
-
-We don't support Sphinx versions before 1.4 since the format of index
-tuples has changed.

cranelift/docs/conf.py

@@ -27,8 +27,8 @@ sys.path.insert(0, os.path.abspath('../lib/codegen/meta-python'))
 
 # -- General configuration ------------------------------------------------
 
-# If your documentation needs a minimal Sphinx version, state it here.
-#
+# We don't support Sphinx versions before 1.4 since the format of index
+# tuples has changed.
 needs_sphinx = '1.4'
 
 # Add any Sphinx extension module names here, as strings. They can be