This adds a new page to lldb.llvm.org that includes a user guide for lldb-dap. The overall structure for documentation: * https://lldb.llvm.org/resources/lldbdap.html - represents the user facing documentation for lldb-dap, a high level overview of lldb-dap and a place we can point users to for basic usage information. * https://lldb.llvm.org/resources/lldbdap-contributing.html - represents the contributing documentation for lldb-dap. * llvm-project/lldb/tools/lldb-dap/README.md - The lldb-dap VSCode Extension specific documentation. This is a first pass at the documentation, I expect to expand on it further as needed.