Optional install instruction for lld

Summary:
Ran into this with devserver on Linux. `lld` might not be installed for Centos8 with clang I guess.

Created from CodeHub with https://fburl.com/edit-in-codehub

Reviewed By: larryliu0820

Differential Revision: D47884220

fbshipit-source-id: f3ed0db564cda8fe8cfd87f421f6e30058a19bd9

Author: digantdesai

docs/website/docs/tutorials/00_setting_up_executorch.md

@@ -94,6 +94,11 @@ You may want to copy the `buck2` binary into your `$PATH` so you can run it as `
 
 The `--show-output` flag will print the path to the executable if you want to run it directly.
 
+If you run into `Stderr: clang-14: error: invalid linker name in argument '-fuse-ld=lld'`, do
+```bash
+conda install -c conda-forge lld
+```
+
 **Step 3: Run a binary**
 
 ```bash