docs: add sub section "Choosing License"

Author: kenjis

user_guide_src/source/extending/composer_packages.rst

@@ -90,6 +90,12 @@ be ``YourVendor``. So you would write like the following::
 
 This setting instructs Composer to autoload the source code for your package.
 
+Choosing License
+================
+
+If you are not familiar with open source licenses, see https://choosealicense.com/.
+Many PHP packages, including CodeIgniter, use the MIT license.
+
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 Preparing Development Tools
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