docs(README): mention that one can limit the number of CPUs

See #6

README.md

@@ -19,7 +19,7 @@ For example, for `x86_64` you could add:
 
 ```toml
 [package.metadata.multivers.x86_64]
-cpus = ["generic", "alderlake", "skylake", "sandybridge", "ivybridge"]
+cpus = ["x86-64", "x86-64-v2", "x86-64-v3", "x86-64-v4", "raptorlake"]
 ```
 
 After building the different versions, it computes a hash of each version and it filters out the duplicates.
@@ -77,6 +77,14 @@ panic = "abort"
 lto = "thin"
 ```
 
+To reduce the total build time, it might be best to limit the set of CPUs for which the project will be built.
+For instance, you can add to your `Cargo.toml` the following section if you build for `x86_64`:
+
+```toml
+[package.metadata.multivers.x86_64]
+cpus = ["x86-64", "x86-64-v2", "x86-64-v3", "x86-64-v4"]
+```
+
 ## Related Work
 
 - If you want to apply this approach only at the function level, take a look at the [multiversion](https://crates.io/crates/multiversion) crate.