Document --ignore-unnamed-heads option

README.md

@@ -198,11 +198,15 @@ Notes/Limitations
 
 hg-fast-export supports multiple branches but only named branches with
 exactly one head each. Otherwise commits to the tip of these heads
-within the branch will get flattened into merge commits. Chris J
-Billington's [hg-export-tool] can help you to handle branches with
-duplicate heads.
-Alternatively, you can use the [head2branch plugin](./plugins/head2branch)
-to create a new named branch from an unnamed head.
+within the branch will get flattened into merge commits. There are a
+few options to deal with this:
+1. Chris J Billington's [hg-export-tool] can help you to handle branches with
+   duplicate heads.
+2. Use the [head2branch plugin](./plugins/head2branch) to create a new named
+   branch from an unnamed head.
+3. You can ignore unnamed heads with the `-ignore-unnamed-heads` option, which
+   is appropriate in situations such as the extra heads being close commits
+   (abandoned, unmerged changes).
 
 hg-fast-export will ignore any files or directories tracked by mercurial
 called `.git`, and will print a warning if it encounters one. Git cannot
@@ -301,4 +305,11 @@ Frequent Problems
   git it looks like you have deleted all files, when in fact they have
   never been checked out. Just do a checkout of the branch you want.
 
+* `Error: repository has at least one unnamed head: hg r<N>`
+
+  By design, hg-fast-export cannot deal with extra heads on a branch.
+  There are a few options depending on whether the extra heads are
+  in-use/open or normally closed. See [Notes/Limitations](#noteslimitations)
+  section for more details.
+
 [hg-export-tool]: https://github.com/chrisjbillington/hg-export-tool