If you want to create new rules to submit to us, we expect them to be in the src/chrome/content/rules directory. That directory also contains a useful script, make-trivial-rule, to create a simple rule for a specified domain. There is also a script called utils/trivial-validate.py, to check all the pending rules for several common errors and oversights. For example, if you wanted to make a rule for the example.com domain, you could run:
cd src/chrome/content/rules
bash ./make-trivial-rule example.com
This would create Example.com.xml, which you could then take a look at and edit based on your knowledge of any specific URLs at example.com that do or don't work in HTTPS. Please have a look at our Ruleset Style Guide where you can find useful tips about finding more subdomains. Our goal is to have as many subdomains covered as we can find.
A more detailed guide about the syntax can be found at EFF.org. For questions see our FAQ page.