[ci skip] tweaks to doc

docs/archaeology.md

@@ -5,7 +5,7 @@ be reproduced a long time into the future (decades, for example).
 
 Stating it doesn't make it true, though.
 
-Originally the intention was to make ybd build definitions all the way back as
+Originally the intention for ybd was to build definitions all the way back as
 far as the move from morphs.git (2014-02-20). But the development of ybd
 exposed some questionable assumptions in morph and in the definitions
 themselves; we had never specified the definitions format, after all. In the
@@ -15,6 +15,8 @@ than make ybd repeat the mistakes.
 For what it's worth, as of 2016-04-10 ybd parses all the way back to baserock-14.40, which was the first tag where the morph files were organised into subdirectories. Going back further could be attempted, if we consider it
 worthwhile to exhume the builds further back.
 
+This is how ybd behaves on various historical versions of ci.morph:
+
 baserock-14.40:
   (no VERSION) stage1-gcc make[2]: *** [lto-compress.o] Error 1