Simplify install instructions (#555)

My 'hot' take is that the goal of the install instructions should be a
single direct recommended way to use the template, with minimal
diversions. Here I've changed the alternative install instructions to
still link to the `cookiecutter` install instructions, but to shorten it
to reduce potential diversion from the recommended way.

Author: dstansby

README.md

@@ -25,20 +25,13 @@ Python packages with our recommended tooling set up and ready to go.
 Some quick instructions for using our template are below.
 We also have a longer [tutorial](./tutorial.md) that has been presented in workshops for researchers at UCL.
 
-If you have [uv] installed, you can use our template with the following one-liner:
+If you have [uv] installed, you can use our template with the following command:
 
 ```sh
 uvx cookiecutter gh:ucl-arc/python-tooling --checkout latest
 ```
 
-Alternatively you can [install cookiecutter] (following the recommended instructions).
-Do this if you don't use [uv], or if you're likely to want to use cookiecutter again.
-
-Then you'll need to run cookiecutter with our template:
-
-```sh
-cookiecutter gh:ucl-arc/python-tooling --checkout latest
-```
+If you don't want to use uv you can [install cookiecutter] using pip, and run the above command without the leading `uvx`.
 
 When [cookiecutter] runs, it will ask you a series of questions to configure your project.
 Type the answer or hit return without typing anything to use the default option (shown in parenthesis).