The most straightforward contributions to this project fall into two categories: Adding a casing option, and adding a wordlist. Otherwise, please take a look at the open issues and see what you'd like to tackle!
In vscode-namegen, casing options require a couple changes. Each casing option has it's own VS Code command, as well as a case in the getWord() function in extension.ts. The enum which defines which casing option a user prefers to choose by default when using the shift + alt + j keyboard shortcut also needs to be updated.
Adding a wordlist is probably the most accessible contribution for newcomers to this project, and newcomers to VS Code extensions in general. Add a wordlist with one entry per line, all lower case, no special characters into the src/wordlists folder. The file must end in .txt. Then in the enum in package.json which defines which wordlist the user prefers as default, add the exact filename without extension.
In the root of the project, there is a build.ps1 file which can be used to build the extension. After building, in VS Code, press F5 and a development testing VS Code window will open with the extension running. Using the -Package switch will generate a .vsix file that you can add to VS Code.