Add multithreading blurb (#195)

* Add multithreading blurb

* Make linter happy

Author: joseph-henry

docs/multithreading.md

@@ -0,0 +1,33 @@
+---
+title: Multithreading
+description: Enable ZeroTier to use multiple physical cores
+---
+
+As of version `1.14.1` ZeroTier is capable of utilizing more than one CPU core for traffic processing. This enables greater total throughput and more efficient use of machines handling large amounts of traffic.
+
+:::info BETA
+This is currently a beta feature and we welcome any feedback and/or test results. For now it is only available for Linux and is disabled by default. It will be ported to FreeBSD, macOS, and Windows in a future release.
+:::
+
+The feature requires manual activation using the `local.conf` file in the same home directory that stores your node’s identity files. If that file is not already present, create it.
+
+### Example usage
+
+```json title="Example local.conf"
+{
+   "settings":
+   {
+       "multicoreEnabled": true,
+       "concurrency": 2,
+       "cpuPinningEnabled": true
+   }
+}
+```
+
+*[See here](https://docs.zerotier.com/config) for more info on how to configure the client using `local.conf`*
+
+### Tip for success
+
+It is recommended that you choose a concurrency level that is reflective of the actual number of physical (not virtual) cores on your machine. For instance, if `nproc` reports `4`, set a concurrency level of `2`. Additionally, enabling [pinning](https://en.wikipedia.org/wiki/Processor_affinity) seems to improve performance in more cases than not.
+
+Multithreading is unlikely to improve performance over the Internet but will over a physical LAN in most cases.

sidebars.js

@@ -227,7 +227,7 @@ module.exports = {
             description: 'ZeroTier is designed to operate on resource constrained devices and under 16MB of memory.',
             slug: '/iot',
           },
-          items: ['lbm', 'compatibility', 'bridging', 'proxy', 'route-between-phys-and-virt'],
+          items: ['lbm', 'multithreading', 'compatibility', 'bridging', 'proxy', 'route-between-phys-and-virt'],
         },
         /* FreeBSD */
         {