docs: add Used by section, ADOPTERS.md and tidy README

ADOPTERS.md

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+# Echo adopters
+
+Open source projects that run on Echo. Each entry links to public source code that depends on Echo directly.
+
+| Organization | Project | What runs on Echo |
+| --- | --- | --- |
+| Beam | [Beta9](https://github.com/beam-cloud/beta9) | API and gateway |
+| Bluesky | [indigo](https://github.com/bluesky-social/indigo) | AT Protocol Relay and network services |
+| Bluesky | [social-app](https://github.com/bluesky-social/social-app/tree/main/bskyweb) | bskyweb, the bsky.app web server |
+| Bytebase | [Bytebase](https://github.com/bytebase/bytebase) | Backend server and API |
+| Chaitin | [MonkeyCode](https://github.com/chaitin/MonkeyCode) | Backend |
+| Chaitin | [PandaWiki](https://github.com/chaitin/PandaWiki) | Backend API |
+| Comfy Org | [ComfyUI Registry](https://github.com/Comfy-Org/registry-backend) | Registry API |
+| ConfigHub | [ConfigHub SDK](https://github.com/confighub/sdk) | Function server |
+| Confluent | [kcp](https://github.com/confluentinc/kcp) | UI API |
+| Digger | [OpenComputer](https://github.com/diggerhq/opencomputer) | API server |
+| Docker | [Docker Agent](https://github.com/docker/docker-agent) | Agent API, chat and A2A servers |
+| Eukarya | [Re:Earth CMS](https://github.com/reearth/reearth-cms) | CMS server |
+| Eukarya | [Re:Earth Flow](https://github.com/reearth/reearth-flow) | API server |
+| Expanso | [Bacalhau](https://github.com/bacalhau-project/bacalhau) | Public API server |
+| Flanksource | [canary-checker](https://github.com/flanksource/canary-checker) | API and webhook server |
+| Flanksource | [config-db](https://github.com/flanksource/config-db) | Server and debug endpoints |
+| Globo | [tsuru RPaaS operator](https://github.com/tsuru/rpaas-operator) | Management API |
+| Hanko | [Hanko](https://github.com/teamhanko/hanko) | Authentication backend |
+| Harness | [Feature Flags Relay Proxy](https://github.com/harness/ff-proxy) | Relay proxy API |
+| Hatchet | [Hatchet](https://github.com/hatchet-dev/hatchet) | API server |
+| IceWhale | [CasaOS](https://github.com/IceWhaleTech/CasaOS) | API server |
+| Komodor | [Komoplane](https://github.com/komodorio/komoplane) | Backend API |
+| LINAGORA | [cozy-stack](https://github.com/linagora/cozy-stack) | Twake Workplace backend |
+| Microsoft | [Azure Container Networking](https://github.com/Azure/azure-container-networking) | Container Networking Service REST API |
+| Microsoft | [Service Fabric Traefik](https://github.com/microsoft/service-fabric-traefik) | Service discovery REST API |
+| monetr | [monetr](https://github.com/monetr/monetr) | API server |
+| NVIDIA | [NVIDIA Cloud Functions](https://github.com/NVIDIA/nvcf) | LLM API gateway |
+| NVIDIA | [Infra Controller](https://github.com/dsx-ai-factory/infra-controller) | REST API |
+| OpenEverest | [OpenEverest](https://github.com/openeverest/openeverest) | API server |
+| Openlane | [Openlane](https://github.com/theopenlane/core) | API server |
+| Pantacor | [Pantacor Hub](https://github.com/pantacor/pantahub-base) | Hub API |
+| Philips | [Terraform Registry](https://github.com/philips-labs/terraform-registry) | Terraform registry server |
+| Platform Engineering Labs | [formae](https://github.com/platform-engineering-labs/formae) | API server |
+| PostHog | [PostHog](https://github.com/PostHog/posthog) | Livestream service |
+| QXIP | [HOMER](https://github.com/sipcapture/homer-app) | Web app and API |
+| Red Hat | [osbuild-composer](https://github.com/osbuild/osbuild-composer) | Image Builder cloud API |
+| Retail AI | [bean](https://github.com/retail-ai-inc/bean) | Go framework built on Echo |
+| ShellHub | [ShellHub](https://github.com/shellhub-io/shellhub) | API and SSH servers |
+| Streamplace | [Streamplace](https://github.com/streamplace/streamplace) | XRPC API |
+| Temporal | [Temporal UI](https://github.com/temporalio/ui) | Web UI server |
+| Xata | [pgstream](https://github.com/xataio/pgstream) | Webhook subscription server |
+| Xata | [Xata](https://github.com/xataio/xata) | Platform API |
+| Yugabyte | [YugabyteDB](https://github.com/yugabyte/yugabyte-db) | yugabyted UI API server |
+| Zapier | [kubechecks](https://github.com/zapier/kubechecks) | Webhook server |
+| Zapier | [tfbuddy](https://github.com/zapier/tfbuddy) | Hooks server |
+
+## Integrations
+
+Observability and error-tracking tools that ship Echo middleware.
+
+| Organization | Integration |
+| --- | --- |
+| Datadog | [dd-trace-go](https://github.com/DataDog/dd-trace-go/tree/main/contrib/labstack/echo.v4) |
+| Elastic | [APM Go agent](https://github.com/elastic/apm-agent-go/tree/main/module/apmechov4) |
+| Honeycomb | [beeline-go](https://github.com/honeycombio/beeline-go/tree/main/wrappers/hnyecho) |
+| IBM Instana | [go-sensor](https://github.com/instana/go-sensor/tree/main/instrumentation/instaecho) |
+| NAVER | [Pinpoint Go agent](https://github.com/pinpoint-apm/pinpoint-go-agent/tree/main/plugin/echov4) |
+| New Relic | [Go agent](https://github.com/newrelic/go-agent/tree/master/v3/integrations/nrecho-v4) |
+| Sentry | [sentry-go](https://github.com/getsentry/sentry-go/tree/master/echo) |
+
+## Add your project
+
+Open a pull request that adds one row to the table above, keeping it sorted by organization. Link to the public repository and say briefly what runs on Echo. The project must depend on Echo directly.
+
+Entries are based on public source code and do not imply endorsement by the organization. To change or remove an entry, open an issue or a pull request.