Split extension guide into developer & operator how-to

Signed-off-by: Natalie Arellano <[email protected]>

Author: Natalie Arellano

content/docs/extension-guide/_index.md

@@ -0,0 +1,12 @@
++++
+title="Specify an image extension at build time"
+weight=101
++++
+
+<!--more-->
+
+No builder can be truly omniscient, and whoever did yours surely was no exception! 
+
+You need to add a little extra spice to the mix with this late-breaking extension, by doing something like:
+
+`pack build [...] --extension=foo [...]`

content/docs/extension-guide/consume-extension/_index.md

@@ -1,13 +1,12 @@
 +++
-title="Specifying an Image Extension in the Builder"
-weight=405
+title="Specify an image extension in a builder"
+weight=101
 +++
 
-<!-- test:suite=dockerfiles;weight=5 -->
-
-### Specifying an Image Extension in the Builder
+<!--more-->
 
 You're pretty sharp, and you know what your buildpack users will need.
+
 That's why you're going to add something similar to the following lines directly to `builder.toml`:
 
 ```
@@ -21,5 +20,3 @@ id = "foo"
 version = "0.0.1"
 uri = "/local/path/to/extension/foo" # can be relative or absolute
 ```
-
-