Easy path to source code

https://www.reddit.com/r/Thunderbird/comments/1pny804/where_is_the_actual_source_code_it_seems_like_the/ makes the point, I think correctly, that it's not trivially easy to get to the source code from any obvious location.

Some possibilities could be:

1. https://developer.thunderbird.net/ - but it first presents several preliminaries sections because it currently presumes the person is going to contribute code or documentation
2. Thunderbird > Help > About
3. Thunderbird > Help > About > Licensing - lacks any pointers to Thunderbird code in the text "All of the source code to this product is available under licenses which are both free and open source. A URL identifying the specific source code used to create this copy can be found on the build configuration page, and you can read instructions on how to download and build the code for yourself."
4. Thunderbird Help > Troubleshooting Information > about:buildconfig > yields a link like https://hg-edge.mozilla.org/releases/comm-beta/rev/b1a35f8a7251dada824abd12b4de3b70e2064be1 where you have to know to click on "files".

Review the developer.thunderbird.net entry point, Thunderbird Help > About and Licensing, and Troubleshooting Information > about:buildconfig, along with the linked Reddit discussion. Determine which existing location should provide the source-code path and document the agreed route, including the relevant links and any needed wording changes.