Add build instructions

Full build instructions (dependencies, environment, commands) would allow more people to work on translations and on service support.

Also, having official instructions would prevent distributions or regression issues in the future.

Thanks,

The issue names no files or tests, so start by locating the repository's build files and existing documentation. Identify the dependencies, environment requirements, and commands needed for a full build, then document them for contributors working on translations and service support. Done means the instructions are complete and can be followed to build the project.

Written by the indexing model from the issue text.