I get that you aren’t expected to have a wealth of primary sources at this point in your career. Masters theses generally can be entirely based on second-hand research, but I sincerely doubt that most advisers would take issue with their students overachieving, provided you practice the diligence due to primary research (keeping interview transcripts and raw data in a form where a person reviewing your work can easily compare them to your delivered paper). Then, if you decide to pursue a PhD, you can point out that your thesis was already high-quality original research, so they’d be stupid to not accept you. That’s how I’d do it.
In this day and age, and especially when the subject is computer science, “online” by itself is not a good reason to exclude sources. That prohibition is a defense against novice researchers who might not know or care how easy it is to put up a web page anonymously with whatever information you desire. But the documentation of a framework like Electron is more akin to a journal produced by the subject of a biography than it is to a poorly-sourced Wikipedia page. If you cite the Brave blog*, that’s like citing a letter from a famous person. Sure, there could be deceit in the text, and it’s guaranteed to be subjective, but it’s useful because it’s the testimony of one of the people working on the subject that you are researching. And unlike historical figures, this is an area where you can verify that anything supposedly written by an interview subject actually was, because you can ask them.
* I picked that one not because you’re necessarily going to have any use for it, but because it’s a very idealistic series of messages that present an argument for the author’s (or authors’) point of view, not unlike the Federalist Papers.