Add documentation about static linking CRT

A section and heading is added to the binary module-level documentation
with details and information about the CRT dependency when using the
MSVC runtime and static linking with the Rust compiler (rustc).

Efforts are underway to make this less of an issue, but for the time
being some recognition of the issue and information on resolution in the
documentation would probably be appreciated by users.

src/main.rs

@@ -25,6 +25,7 @@
 //! ## Table of Contents
 //!
 //! - [Quick Start](#quick-start)
+//! - [C Runtime](#c-runtime)
 //! - [Examples](#examples)
 //! - [Features](#features)
 //!   - [Signing](#signing)
@@ -73,6 +74,41 @@
 //! installation destination is `C:\Program Files\<project name>`, where
 //! `<project name>` is replaced with the name of the project.
 //!
+//! ## C Runtime
+//!
+//! If using the `x86_64-pc-windows-msvc` or the `i686-pc-windows-msvc`
+//! toolchain, then an appropriate C RunTime (CRT) must be available on the host
+//! system _or_ the CRT must be statically compiled with the Rust binary
+//! (executable). By default, the CRT is dynamically linked to a Rust binary. This
+//! may cause issues and errors when running the Rust binary immediately after
+//! installation on a clean Windows installation, i.e. the CRT has not already been
+//! installed. If the Rust compiler is installed and an `-msvc` toolchain is
+//! available, then the Rust binary will execute after installation without an
+//! issue. 
+//! 
+//! **Note**, the Rust programming language does _not_ need to be installed
+//! to run an executable built using Cargo and Rust. Only a Microsoft provided CRT
+//! needs to be installed. These are often referred to as "redistributables". Rust
+//! with either of the `-msvc` toolchains currently dynamically links against the
+//! `vcruntime140.dll`, which is part of the Visual C++ 2015 redistributable and
+//! freely provided by Microsoft.
+//!
+//! For developers using the `cargo-wix` subcommand to create an installer, this
+//! dependency on the present of an appropriate C runtime can lead to a sub-optimal
+//! user experience. There are three options: (i) statically link the C runtime
+//! within the Rust binary (recommended), (ii) add the Visual C++ redistributable to
+//! the installer via the [Merge module] method for the WiX Toolset, or (iii)
+//! provide the user with instructions for downloading and installing the CRT
+//! _before_ running the executable. The currently recommended option is to
+//! [statically link the CRT] when building the Rust binary. Rust v1.19 or newer is
+//! required, and the solution ultimately becomes adding the `-C target-feature=+crt-static` 
+//! option to the invocation of the Rust compiler (rustc). There are a variety
+//! of methods for adding the option to the invocation, including but not
+//! limited to adding a configuration directive to the pacakge's manifest, using the
+//! `RUSTFLAGS` environment variable, or adding to the user's Cargo
+//! configuration. Please see the Rust compiler documentation on static linking
+//! for more information and details.
+//!
 //! ## Examples
 //!
 //! All of the following examples use the native Command Prompt (cmd.exe) for
@@ -1085,6 +1121,7 @@
 //! [LibreOffice]: https://www.libreoffice.org/
 //! [`license`]: https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata
 //! [`license-file`]: https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata
+//! [Merge module]: https://wixtoolset.org/documentation/manual/v3/howtos/redistributables_and_install_checks/install_vcredist.html
 //! [Microsoft Office]: https://products.office.com/en-us/home
 //! [Microsoft Notepad]: https://en.wikipedia.org/wiki/Microsoft_Notepad
 //! [PowerShell]: https://github.com/PowerShell/PowerShell
@@ -1093,6 +1130,7 @@
 //! [Rust]: https://www.rust-lang.org
 //! [sidecar]: https://en.wikipedia.org/wiki/Sidecar_file
 //! [SignTool]: https://msdn.microsoft.com/en-us/library/windows/desktop/aa387764(v=vs.85).aspx
+//! [statically link the CRT]: https://doc.rust-lang.org/reference/linkage.html#static-and-dynamic-c-runtimes
 //! [`std::process::Command`]: https://doc.rust-lang.org/std/process/struct.Command.html
 //! [`std::process::Command::status`]: https://doc.rust-lang.org/std/process/struct.Command.html#method.status
 //! [TOML array]: https://github.com/toml-lang/toml#user-content-array