Update README install instructions to use pipx (#877)

Co-authored-by: Michal Wojcik <32574975+mgwoj@users.noreply.github.com>
Co-authored-by: Zhiwei Liang <121905282+zliang-akamai@users.noreply.github.com>

Author: 3 people

README.md

@@ -12,12 +12,21 @@ Visit the [Wiki](../../wiki) for more information.
 
 ## Install
 
-Install via PyPI:
+We recommend installing `linode-cli` with `pipx`, which installs each Python CLI tool into its own isolated environment and works on distributions where `pip install` fails because the system Python is marked as externally managed ([PEP 668](https://peps.python.org/pep-0668/)). If pipx isn't installed yet, follow the [pipx installation guide](https://pipx.pypa.io/latest/how-to/install-pipx.html).
+
+To install:
+
+```bash
+pipx install linode-cli
+```
+
+To upgrade:
+
 ```bash
-pip3 install linode-cli
+pipx upgrade linode-cli
 ```
 
-Visit the [Wiki](../../wiki/Installation) for more information.
+The [Wiki](https://github.com/linode/linode-cli/wiki/Installation) covers other installation methods, including the Docker image, the GitHub Action, and building from source.
 
 ## Contributing