document targetFeatures better

I initially misinterpreted this as a hook to influence the list of
features a crate is built with, depending on the target, but this is
just the strings passed to `rustc`'s `-C target-feature=`.`

crate2nix/Cargo.nix

@@ -14,6 +14,8 @@
 , rootFeatures ? [ "default" ]
   # If true, throw errors instead of issueing deprecation warnings.
 , strictDeprecation ? false
+  # Elements to add to the `-C target-feature=` argument passed to `rustc`
+  # (separated by `,`, prefixed with `+`).
   # Used for conditional compilation based on CPU feature detection.
 , targetFeatures ? []
   # Whether to perform release builds: longer compile times, faster binaries.

crate2nix/templates/Cargo.nix.tera

@@ -16,6 +16,8 @@
 , rootFeatures ? [ "default" ]
   # If true, throw errors instead of issueing deprecation warnings.
 , strictDeprecation ? false
+  # Elements to add to the `-C target-feature=` argument passed to `rustc`
+  # (separated by `,`, prefixed with `+`).
   # Used for conditional compilation based on CPU feature detection.
 , targetFeatures ? []
   # Whether to perform release builds: longer compile times, faster binaries.

sample_projects/bin_with_git_submodule_dep/Cargo.nix

@@ -14,6 +14,8 @@
 , rootFeatures ? [ "default" ]
   # If true, throw errors instead of issueing deprecation warnings.
 , strictDeprecation ? false
+  # Elements to add to the `-C target-feature=` argument passed to `rustc`
+  # (separated by `,`, prefixed with `+`).
   # Used for conditional compilation based on CPU feature detection.
 , targetFeatures ? []
   # Whether to perform release builds: longer compile times, faster binaries.

sample_projects/codegen/Cargo.nix

@@ -14,6 +14,8 @@
 , rootFeatures ? [ "default" ]
   # If true, throw errors instead of issueing deprecation warnings.
 , strictDeprecation ? false
+  # Elements to add to the `-C target-feature=` argument passed to `rustc`
+  # (separated by `,`, prefixed with `+`).
   # Used for conditional compilation based on CPU feature detection.
 , targetFeatures ? []
   # Whether to perform release builds: longer compile times, faster binaries.

sample_projects/sub_dir_crates/Cargo.nix

@@ -14,6 +14,8 @@
 , rootFeatures ? [ "default" ]
   # If true, throw errors instead of issueing deprecation warnings.
 , strictDeprecation ? false
+  # Elements to add to the `-C target-feature=` argument passed to `rustc`
+  # (separated by `,`, prefixed with `+`).
   # Used for conditional compilation based on CPU feature detection.
 , targetFeatures ? []
   # Whether to perform release builds: longer compile times, faster binaries.