Fix installation for Ubuntu in README.md (#4031)

- **PR Description**
If '/usr/local/bin' does not exist, 'install' will eventually result in
a regular file named '/usr/local/bin' being created.

- **Please check if the PR fulfills these requirements**

* [ ] Cheatsheets are up-to-date (run `go generate ./...`)
* [ ] Code has been formatted (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#code-formatting))
* [ ] Tests have been added/updated (see
[here](https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md)
for the integration test guide)
* [ ] Text is internationalised (see
[here](https://github.com/jesseduffield/lazygit/blob/master/CONTRIBUTING.md#internationalisation))
* [ ] If a new UserConfig entry was added, make sure it can be
hot-reloaded (see
[here](https://github.com/jesseduffield/lazygit/blob/master/docs/dev/Codebase_Guide.md#using-userconfig))
* [ ] Docs have been updated if necessary
* [x] You've read through your own file changes for silly mistakes etc

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Author: jesseduffield

README.md

@@ -309,7 +309,7 @@ sudo eopkg install lazygit
 LAZYGIT_VERSION=$(curl -s "https://api.github.com/repos/jesseduffield/lazygit/releases/latest" | grep -Po '"tag_name": "v\K[^"]*')
 curl -Lo lazygit.tar.gz "https://github.com/jesseduffield/lazygit/releases/latest/download/lazygit_${LAZYGIT_VERSION}_Linux_x86_64.tar.gz"
 tar xf lazygit.tar.gz lazygit
-sudo install lazygit /usr/local/bin
+sudo install lazygit -D -t /usr/local/bin/
 ```
 
 Verify the correct installation of lazygit: