docs: Update install instructions (ignite#794)

* Update install instructions

* Update docs/1 Introduction/2 Install.md

Author: Alessio Treglia

docs/1 Introduction/2 Install.md

@@ -10,6 +10,18 @@ curl https://get.starport.network/starport! | bash
 
 This command will download the latest `starport` binary from Github and install it into `/usr/local/bin`. To learn more about how to install previous versions of the binary, refer to the [documentation](https://github.com/allinbits/starport-installer).
 
+If the installer fails due to `/usr/local/bin/` not being writable by the user, then execute the following command:
+
+```
+curl https://get.starport.network/starport | bash
+```
+
+Finally, move the `starport` executable to `/usr/local/bin/` manually:
+
+```
+sudo mv starport /usr/local/bin/
+```
+
 ## macOS with Homebrew
 
 ```