This may become more fleshed out in the future if needed.
Right now there are no formal code style guidelines. Just follow the current style as best as you can.
Your contributions must be compatible with the license of the project. Please note that the license is GPLv3 with an app store exception, i.e. you allow your code to be included in a build published on an app store, even if the app store has terms incompatible with the GPL. This generally excludes code that comes from a GPLv3 codebase.
To show that you understand this, you must sign-off any commits you include in a pull request. You can do this from the command line with git commit -s. If you want to do this manually instead, include the following line at the bottom of all commit messages:
Signed-off-by: Your Name <youremail@example.com>
By signing-off your commit(s), you agree to the Developer Certificate of Origin, the text of which is below:
Developer Certificate of Origin
Version 1.1
Copyright (C) 2004, 2006 The Linux Foundation and its contributors.
Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.
Developer's Certificate of Origin 1.1
By making a contribution to this project, I certify that:
(a) The contribution was created in whole or in part by me and I
have the right to submit it under the open source license
indicated in the file; or
(b) The contribution is based upon previous work that, to the best
of my knowledge, is covered under an appropriate open source
license and I have the right under that license to submit that
work with modifications, whether created in whole or in part
by me, under the same open source license (unless I am
permitted to submit under a different license), as indicated
in the file; or
(c) The contribution was provided directly to me by some other
person who certified (a), (b) or (c) and I have not modified
it.
(d) I understand and agree that this project and the contribution
are public and that a record of the contribution (including all
personal information I submit with it, including my sign-off) is
maintained indefinitely and may be redistributed consistent with
this project or the open source license(s) involved.
Note that "signing" your commit is different from "signing-off" your commit. Signing your commit, such as with a GPG or SSH signature, is not required but welcome.