v0.9.x: document mercurial dependency for operators (#1683) (#1684)

* README.md,doc/user-guide.md: add mercurial v3.9+ dependency for new operator projects

* CHANGELOG.md: add mercurial documentation addition

CHANGELOG.md

@@ -1,3 +1,17 @@
+## Unreleased
+
+### Added
+
+- Document new compile-time dependency `mercurial` in user-facing documentation. ([#1683](https://github.com/operator-framework/operator-sdk/pull/1683))
+
+### Changed
+
+### Deprecated
+
+### Removed
+
+### Bug Fixes
+
 ## v0.9.0
 
 ### Added

README.md

@@ -40,6 +40,7 @@ The following workflow is for a new **Helm** operator:
 
 - [git][git_tool]
 - [go][go_tool] version v1.12+.
+- [mercurial][mercurial_tool] version 3.9+
 - [docker][docker_tool] version 17.03+.
   - Alternatively [podman][podman_tool] `v1.2.0+` or [buildah][buildah_tool] `v1.7+`
 - [kubectl][kubectl_tool] version v1.11.3+.
@@ -172,6 +173,7 @@ Operator SDK is under Apache 2.0 license. See the [LICENSE][license_file] file f
 [dep_tool]:https://golang.github.io/dep/docs/installation.html
 [git_tool]:https://git-scm.com/downloads
 [go_tool]:https://golang.org/dl/
+[mercurial_tool]:https://www.mercurial-scm.org/downloads
 [docker_tool]:https://docs.docker.com/install/
 [podman_tool]:https://github.com/containers/libpod/blob/master/install.md
 [buildah_tool]:https://github.com/containers/buildah/blob/master/install.md

doc/user-guide.md

@@ -7,6 +7,7 @@ This guide walks through an example of building a simple memcached-operator usin
 
 - [git][git_tool]
 - [go][go_tool] version v1.12+.
+- [mercurial][mercurial_tool] version 3.9+
 - [docker][docker_tool] version 17.03+.
 - [kubectl][kubectl_tool] version v1.11.3+.
 - Access to a Kubernetes v1.11.3+ cluster.
@@ -609,6 +610,7 @@ When the operator is not running in a cluster, the Manager will return an error
 [git_tool]:https://git-scm.com/downloads
 [go_tool]:https://golang.org/dl/
 [docker_tool]:https://docs.docker.com/install/
+[mercurial_tool]:https://www.mercurial-scm.org/downloads
 [kubectl_tool]:https://kubernetes.io/docs/tasks/tools/install-kubectl/
 [minikube_tool]:https://github.com/kubernetes/minikube#installation
 [scheme_package]:https://github.com/kubernetes/client-go/blob/master/kubernetes/scheme/register.go