Document --no-color and --color options to sphinx-build (#11443)

Author: chrysle

doc/man/sphinx-build.rst

@@ -201,10 +201,19 @@ Options
    references.  See the config value :confval:`nitpick_ignore` for a way to
    exclude some references as "known missing".
 
-.. option:: -N
+.. option:: -N, --no-color
 
    Do not emit colored output.
 
+   .. versionchanged:: 1.6
+      Add ``--no-color`` long option.
+
+.. option:: --color
+
+   Emit colored output. Auto-detected by default.
+
+   .. versionadded:: 1.6
+
 .. option:: -v
 
    Increase verbosity (loglevel).  This option can be given up to three times