docs: add troubleshooting page (#1752)

* docs: add troubleshooting page

* docs: add link to personal access token

* docs: add install command

README.md

@@ -219,6 +219,10 @@ Contributions welcome! See the [Contributing Guide](https://github.com/googleapi
 
 For more information on the design of the library, see [design](https://github.com/googleapis/release-please/blob/main/docs/design.md).
 
+## Troubleshooting
+
+For common issues and help troubleshooting your configuration, see [Troubleshooting](https://github.com/googleapis/release-please/blob/main/docs/troubleshooting.md).
+
 ## License
 
 Apache Version 2.0

docs/troubleshooting.md

@@ -0,0 +1,109 @@
+# Troubleshooting
+
+## Debugging with the CLI
+
+The easiest way to debug your `release-please` configuration is to use the bundled
+CLI. 
+
+To use the CLI, you will need to use a GitHub
+[personal access token](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token):
+
+```bash
+# install the release-please binary
+npm install -g release-please
+
+export GITHUB_TOKEN="my-access-token"
+release-please release-pr \
+  --token=${GITHUB_TOKEN} \
+  --repo-url=my-owner/my-repo \
+  --debug \
+  --dry-run
+```
+
+The CLI provides a `--dry-run` mode which will tell you what it would do without
+actually doing it (i.e. without opening a pull request or tagging releases).
+Additionally, we provide log level options `--debug` or `--trace` which will
+show more in-depth logging and should help give you insight into what `release-please`
+is trying to do.
+
+### Testing in another branch
+
+When testing out a new change to the `release-please-config.json`, make the change
+in a new branch on the actual repository (not a fork). `release-please` relies on
+pull requests, releases, and tags which are not copied when you fork the original
+repository.
+
+After pushing your change to the new branch, you can target the new branch using
+the `--target-branch` option.
+
+```bash
+export GITHUB_TOKEN="my-access-token"
+release-please release-pr \
+  --token=${GITHUB_TOKEN} \
+  --repo-url=my-owner/my-repo \
+  --target-branch=my-test-branch \
+  --debug \
+  --dry-run
+```
+
+## Frequently Asked Questions
+
+### What is a component?
+
+A component is an individually releasable artifact or group of
+artifacts within a repository.
+
+The most common configuration is for a single repository to
+release a single package. In this case, the releases and tags
+with have simple versions like `v1.2.3`. In this case, you
+will not need to configure a `component` in the configuration.
+
+In the case of a monorepo, you may have separate, independently
+releaseable artifacts. In this case, the releases will use a
+`component` prefix for the release and tag like
+`my-component-v1.2.3`. This allows you to have separate releases
+and tags for each component for version `1.2.3`.
+
+You will need to configure a `component` name in the manifest
+config for each of your independent modules (separated by
+code path):
+
+```json
+{
+  "packages": {
+    "path/to/pkg-a": {
+      "component": "pkg-a"
+    },
+    "path/to/pkg-b": {
+      "component": "pkg-b"
+    }
+  }
+}
+```
+
+### How does release-please determine the previous release?
+
+#### If you are using a manifest config (highly advised)
+
+`release-please` reads the latest released version from the
+manifest file (`.release-please-manifest.json`). The file is a map
+of component path to the latest release version. In a single
+component setup, the path should be `.`. `release-please` tries to
+identify the commit SHA of that release version by looking at
+recent releases and falling back to looking at the expected tag name.
+
+#### If you are NOT using a manifest config
+
+`release-please` uses a few methods to try determine the latest
+release. Note that this process can be fragile and will require
+more API calls (which is one reason a manifest config is preferred).
+
+1. Iterate through the last 250 commits on the target branch and
+   look for an associated release pull request. If found, extract
+   the latest release version from that pull request.
+2. Iterate through the latest releases and compare against commit
+   SHAs seen in the last 250 commits on the target branch. This
+   is to ensure that the release happened on this target branch.
+3. Iterate through the latest tags and compare against commit
+   SHAs seen in the last 250 commits on the branch. This is to
+   ensure that the tag happened on this target branch.