ICU-21546 brs 69, add note about genren process

diff --git a/icu4c/source/tools/genren/README b/icu4c/source/tools/genren/README
index e2e13bc3ed1cc890847cfc7696c7efec676981bb..a18c294136ddd5e37020ae19376412816b74d504 100644 (file)
--- a/icu4c/source/tools/genren/README
+++ b/icu4c/source/tools/genren/README
@@ -20,6 +20,14 @@ This is prerequisite for the icu layoutex (Paragraph Layout) project, which is s
     cd icu4c/source
     svn export https://github.com/behdad/icu-le-hb/trunk/src layout
 
+(As an alternative to the above handling of layout engine header files, you can do the following:
+1. In the Makefile in this directory, temporarily delete $(LEX) from the list of objects for LIBS
+   before running make install-header
+2. After running make install-header, restore the deleted $(LEX) in the Makefile
+3. Then when comparing the old urename.h to the newly generated one, copy all of the lines beginning
+   "#define pl_" from the old version to the new one.
+ - Peter E)
+
 - Regenerate urename.h
 
     cd icu4c/source/tools/genren