Add note to docs about sharp memory usage on default Linux setup

It's fairly opaque to the user that there are problems with `sharp` in an out-of-the-box Linux environment, and so if `sharp` is going to be explicitly recommended for non-Vercel production environments then I think it's a good idea to make sure people are aware of the possible issues.

My vanilla Heroku deployment was using wild amounts of memory until I found the details in the sharp docs about how to configure the memory allocator, so signposting this a bit better should help prevent issues in future.

docs/deployment.md

@@ -76,7 +76,7 @@ Next.js can be deployed to any hosting provider that supports Node.js. Make sure
 
 `next build` builds the production application in the `.next` folder. After building, `next start` starts a Node.js server that supports [hybrid pages](/docs/basic-features/pages.md), serving both statically generated and server-side rendered pages.
 
-If you are using [`next/image`](/docs/basic-features/image-optimization.md), consider adding `sharp` for more performant [Image Optimization](/docs/basic-features/image-optimization.md) in your production environment by running `npm install sharp` in your project directory.
+If you are using [`next/image`](/docs/basic-features/image-optimization.md), consider adding `sharp` for more performant [Image Optimization](/docs/basic-features/image-optimization.md) in your production environment by running `npm install sharp` in your project directory. Note that on Linux platforms sharp may require [some additional configuration](https://sharp.pixelplumbing.com/install#linux-memory-allocator) to prevent excessive memory usage.
 
 ### Docker Image