document raw

README.md

@@ -117,6 +117,7 @@ you MAY set these variables:
  - `TAGS` (as an array!)
  - `DONT_CACHE` (to explicitly not cache the rendered blag)
  - `WRITTEN_AT` (if the filesystem/libc doesn't support it)
+ - `RAW` (see [raw responses](#raw_responses))
 
 you SHOULD NOT set `MODIFIED_AT` unless you have a valid reason.
 
@@ -129,6 +130,13 @@ safely use `jq` to parse it.
 
 the rest is normal
 
+### raw responses
+
+if you set `RAW` to a non-empty value, bingus-blog will abort normal
+function and instead respond with whatever your script outputted, setting
+the Content-Type header to the value of `RAW`. this can be used to implement
+APIs in blag (do not do this).
+
 ### cache invalidation
 
 due to how blag works, the hash of the query params is stored alongside the