Update installation docs (#2840)

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Closes #

## Introduced changes

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## Checklist

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- [x] Linked relevant issue
- [x] Updated relevant documentation
- [x] Added relevant tests
- [x] Performed self-review of the code
- [x] Added changes to `CHANGELOG.md`

Author: kkawula

docs/src/getting-started/installation.md

@@ -107,6 +107,12 @@ Install Scarb
 asdf install scarb latest
 ```
 
+Set a version globally (in your ~/.tool-versions file):
+
+```shell
+asdf global scarb latest
+```
+
 To verify that Scarb was installed, run
 
 ```shell
@@ -129,6 +135,12 @@ Install Starknet Foundry
 asdf install starknet-foundry latest
 ```
 
+Set a version globally (in your ~/.tool-versions file):
+
+```shell
+asdf global starknet-foundry latest
+```
+
 To verify that Starknet Foundry was installed, run
 
 ```shell