Add Spack logo.

README.md

-Spack
-===========
+![image](share/spack/logo/spack-logo-text-64.png "Spack")
+============
 
 Spack is a package management tool designed to support multiple
 versions and configurations of software on a wide variety of platforms

lib/spack/docs/conf.py

@@ -149,7 +149,7 @@
 # Theme options are theme-specific and customize the look and feel of a theme
 # further.  For a list of options available for each theme, see the
 # documentation.
-#html_theme_options = [('show_copyright', False)]
+html_theme_options = { 'logo_only' : True }
 
 # Add any paths that contain custom themes here, relative to this directory.
 html_theme_path = ["_themes"]
@@ -163,12 +163,12 @@
 
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.
-#html_logo = None
+html_logo = '../../../share/spack/logo/spack-logo-white-text-48.png'
 
 # The name of an image file (within the static path) to use as favicon of the
 # docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
 # pixels large.
-#html_favicon = None
+html_favicon = '../../../share/spack/logo/favicon.ico'
 
 # Add any paths that contain custom static files (such as style sheets) here,
 # relative to this directory. They are copied after the builtin static files,