update README

README.md

@@ -1,8 +1,19 @@
 # perl
+
 Custom compiled perl for Binary.com
 
-# compiling steps
+## compiling steps
 
+```bash
 BRANCH=perl-5.26.1 ./rebuild.sh
-
 ```
+
+## compiling it with CI
+
+1. enable CI test in your forked repo : 
+   at https://github.com/username/perl/settings/actions set `Allow all actions and reusable workflows`
+   and `Read and write permissions`. Don't forget to click `save` at both section.
+2. Or create a new branch directly on binary-com/perl repo
+3. create a branch whose name include a perl version `perl-x.yy.zz`, e.g. `upgrade/perl.5.38.2`
+
+Then CI will download and compile perl and push it to your branch