gh-help: add page (#5129)

pages/common/gh-help.md

@@ -0,0 +1,28 @@
+# gh help
+
+> Display help about the GitHub CLI command.
+> More information: <https://cli.github.com/manual/gh_help>.
+
+- Display general help:
+
+`gh help`
+
+- Display help for the `gh help` subcommand:
+
+`gh help --help`
+
+- Display help about environment variables that can be used with `gh`:
+
+`gh help environment`
+
+- Display a markdown reference of all `gh` commands:
+
+`gh help reference`
+
+- Display help for a subcommand:
+
+`gh help {{subcommand}}`
+
+- Display help for a subcommand action:
+
+`gh help {{pr}} {{create}}`