Add rationale

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+Why not innfeed ?
+
+Two reasons:
+
+1. innfeed is not reliable[1].  In particular, the program feed
+   protocol spoken between innd and innfeed is lossy: if innfeed dies
+   unexpectedly, articles which innd has written to the pipe to
+   innfeed will be skipped.  innd has no way of telling which articles
+   those are, no useful records, and no code to retry.  I can see no
+   sensible way to solve this problem without using a different
+   approach to getting articles from innd.
+
+ [1] By "reliable" I mean that articles will be propagated unless
+     either (a) there is some deliberate policy or technical reason
+     why they are not or (b) transient problems prevent the
+     propagation from succeeding before the article expires.
+
+2. Why not just edit innfeed ?  Well, innfeed is an very large program
+   for what it does - nearly 25kloc.
+
+So I set out to write something similar but smaller and reliable.