Add note about Arch AUR `packer` package.

Closes #6718

website/source/intro/getting-started/install.html.md

@@ -114,7 +114,7 @@ install Packer by running:
 
 ## Troubleshooting
 
-On some RedHat-based Linux distributions there is another tool named `packer`
+On some *RedHat*-based Linux distributions there is another tool named `packer`
 installed by default. You can check for this using `which -a packer`. If you get
 an error like this it indicates there is a name conflict.
 
@@ -125,3 +125,8 @@ an error like this it indicates there is a name conflict.
 To fix this, you can create a symlink to packer that uses a different name like
 `packer.io`, or invoke the `packer` binary you want using its absolute path,
 e.g. `/usr/local/packer`.
+
+On *Arch* Linux there is a package named `packer` in the main
+repository and in the AUR. The package `packer` in the AUR is an old
+name for a package management tool for Arch, it's not Hashicorp
+Packer.