import-hg: Mention tag and branch mapping files

Users frequently submit summarily rejected patches doing some magit
branch and tag name munging to the hg-fast-export project instead of
using a mapping file. Try to prevent wasted work by mentioning the
existence of mapping files for branches and tags when author mapping
files are covered.

Author: frej

book/09-git-and-other-scms/sections/import-hg.asc

@@ -52,6 +52,8 @@ In this example, we want our file to look like this:
 "bob jones <bob <AT> company <DOT> com>"="Bob Jones <[email protected]>"
 ----
 
+The same kind of mapping file can be used to rename branches and tags when the Mercurial name is not allowed by Git.
+
 The next step is to create our new Git repository, and run the export script:
 
 [source,console]
@@ -61,7 +63,7 @@ $ cd /tmp/converted
 $ /tmp/fast-export/hg-fast-export.sh -r /tmp/hg-repo -A /tmp/authors
 ----
 
-The `-r` flag tells hg-fast-export where to find the Mercurial repository we want to convert, and the `-A` flag tells it where to find the author-mapping file.
+The `-r` flag tells hg-fast-export where to find the Mercurial repository we want to convert, and the `-A` flag tells it where to find the author-mapping file (branch and tag mapping files are specified by the `-B` and `-T` flags respectively).
 The script parses Mercurial changesets and converts them into a script for Git's "fast-import" feature (which we'll discuss in detail a bit later on).
 This takes a bit (though it's _much_ faster than it would be over the network), and the output is fairly verbose: