Add overview of tools to README.md (open-telemetry#1022)

Resolve open-telemetry#1008

Author: MrAlias

README.md

@@ -8,3 +8,123 @@ Build tools for use by the Go API/SDK, the collector, and their associated
 contrib repositories
 
 [Contributing](CONTRIBUTING.md)
+
+## Tools
+
+This repository provides tooling for OpenTelemetry Go projects. Below are
+overviews and examples of each provided tools:
+
+### [`gotmpl`](./gotmpl/README.md)
+
+`gotmpl` generates files from Go templates and JSON data.
+
+```sh
+gotmpl --body=template.tmpl --data='{"key":"value"}' --out=output.go
+```
+
+`gotmpl` is designed to be used with `go generate` to generate code or
+configuration files from templates.
+
+```go
+//go:generate gotmpl --body=../internal/shared/env.go.tmpl "--data={ \"pkg\": \"jaeger\" }" --out=env.go
+```
+
+### [`issuegenerator`](./issuegenerator/README.md)
+
+Generates an issue if any test fails in CI.
+
+### [`chloggen`](./chloggen/README.md)
+
+Generates a `CHANGELOG` file from individual change YAML files.
+
+```sh
+# generates a new change YAML file from a template
+chloggen new -filename <filename>
+# validates all change YAML files
+chloggen validate
+# provide a preview of the generated changelog file
+chloggen update -dry
+# updates the changelog file
+chloggen update -version <version>
+```
+
+### [`checkapi`](./checkapi/README.md)
+
+Analyzes a Go module's API surface and enforces restrictions.
+
+```sh
+checkapi -folder . -config config.yaml
+```
+
+### [`crosslink`](./crosslink/README.md)
+
+Manages multiple `go.mod` files and intra-repository dependencies.
+
+```sh
+# Insert/overwrite replace statements for intra-repo dependencies
+crosslink --root=/path/to/repo
+
+# Remove unnecessary replace statements
+crosslink prune
+crosslink --root=/path/to/repo --prune
+
+# Overwrite existing replace statements
+crosslink --root=/path/to/repo --overwrite
+
+# Generate or update go.work file
+crosslink work --root=/path/to/repo
+```
+
+### [`checkfile`](./checkfile/README.md)
+
+Checks that components in OpenTelemetry core and contrib repos contain a
+required file.
+
+```sh
+checkfile --project-path path/to/project \
+          --component-rel-path service/defaultcomponents/defaults.go \
+          --module-name go.opentelemetry.io/collector \
+          --file-name README.md
+```
+
+### [`githubgen`](./githubgen/README.md)
+
+Generates `.github/CODEOWNERS` and `.github/ALLOWLIST` files.
+
+```sh
+githubgen --skipgithub --folder . --github-org "open-telemetry" \
+  --default-codeowner open-telemetry/opentelemetry-collector-approvers \
+  --allowlist cmd/githubgen/allowlist.txt
+```
+
+To authenticate for GitHub API, set a `GITHUB_TOKEN` environment variable.
+
+### [`dbotconf`](./dbotconf/README.md)
+
+`dbotconf` is a Go-based tool for management of [dependabot] configuration. It
+provides the `generate` and `verify` commands to create and validate
+[dependabot configuration files].
+
+```sh
+# Generate configuration files
+dbotconf generate
+
+# Verify existing configuration files
+dbotconf verify
+```
+
+[dependabot]: https://github.com/dependabot
+[dependabot configuration files]: https://docs.github.com/en/code-security/dependabot/working-with-dependabot/dependabot-options-reference#about-the-dependabotyml-file
+
+### [`multimod`](./multimod/README.md)
+
+Tooling to support versioning of multiple Go modules in a repository.
+
+```sh
+# Verify module versioning configuration.
+./multimod verify
+# Prepare a pre-release commit.
+./multimod prerelease --module-set-name <name>
+# Tag the new release commit.
+./multimod tag --commit-hash <hash>
+```