Add deps to iohook docs

docs/native-node-modules.md

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+# Native Node Modules
+
+Since v???, the electron version of Riot can make use of native node modules.
+These allow Riot to integrate with the desktop in ways that a browser cannot.
+
+While handy, these modules must be compiled and are thus downloaded
+pre-compiled during build so that a single OS can compile Riot for all
+platforms. If you would like to compile the native node modules from source,
+as is done for Riot releases, instead of trusting binaries hosted on npm,
+then please read on.
+
+Do note that compiling a module for a particular operating system
+(Linux/Mac/Windows) and will need to be done on that operating system.
+
+## Compiling iohook
+
+[iohook](https://github.com/matrix-org/iohook/) is a native node module
+written in C/C++ that allows for cross-platform capturing of keystrokes. This
+is used for providing Push-to-Talk functionality (pressing a key to toggle
+the microphone in a call) and is ONLY enabled during a call and while setting
+the keybinding in settings.
+
+If you would like to rebuild the module yourself and replace the downloaded
+binaries, then first make sure you have the following dependencies:
+
+**Common:**
+- `npm`, `yarn`
+
+**Linux:**
+- `apt install build-essentials cmake`
+
+**MacOS:**
+- Xcode developer tools
+- `brew`
+- Then `brew install cmake automake libtool pkg-config`
+
+**Windows:**
+- unsupported
+
+Then simply execute `build-native-modules.sh` with the following flags:
+
+```bash
+./scripts/build-native-modules.sh -e 4.2.6 -a 69 -i
+```
+
+`-e` specifies the electron version. Note that the latest electron version can
+always be found in riot-web's `package.json`. `-a` specifies the electron ABI
+version, and `-i` tells the script to build iohook and then install it.
+
+If you'd just like to build the module without installing it, use `-I` instead.
+
+```bash
+./scripts/build-native-modules.sh -e 4.2.6 -a 69 -I
+```
+
+To start Riot web, use `npx electron .`. To package, use `build -wml -ia32 --x64`.