Update exclude_path description and examples

Now that we use cargo-llvm-cov, `exclude_path` should be a regular
expression, since we are using `--ignore-filename-regex` option:

   --ignore-filename-regex <PATTERN>
       Skip source code files with file paths that match the given
       regular expression

To prevent users from separating multiple files with commas,
let's update the `exclude_path` description in the README and in
the examples.

Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>

README.md

@@ -37,10 +37,11 @@ found in
 The json must have the following fields:
 
 - `coverage_score`: The coverage of the repository.
-- `exclude_path`: This field is used for excluding files from the report. It
-  should be used to exclude autogenerated files. Files in `exclude_path` are
-  separated by one comma. If the repository does not have any autogenerated
-  files, `exclude_path` should be an empty string.
+- `exclude_path`: This field is used for excluding files from the report.
+  File paths that match the given regular expression are skipped. (for example,
+  if multiple files are to be skipped, they must be separated with `|`).
+  It should be used to exclude autogenerated files. If the repository does not
+  have any autogenerated files, `exclude_path` should be an empty string.
 - `crate_features`: `cargo kcov` does not build crate features by default. To
   get the coverage report including optional features, these need to be
   specified in `crate_features` separated by comma. If the crate does not have

coverage_config_aarch64.json.sample

@@ -1,5 +1,5 @@
 {
   "coverage_score": 90,
-  "exclude_path": "my_autogenerated_file.rs,second_file.rs",
+  "exclude_path": "my_autogenerated_file\\.rs|path/to/my_folder",
   "crate_features": "my_dummy_feature,dummy_feature2"
 }

coverage_config_x86_64.json.sample

@@ -1,5 +1,5 @@
 {
   "coverage_score": 90,
-  "exclude_path": "my_autogenerated_file.rs,second_file.rs",
+  "exclude_path": "my_autogenerated_file\\.rs|path/to/my_folder",
   "crate_features": "my_dummy_feature,dummy_feature2"
 }