Add README for local installer. (#1540)

installers/local/BUILD

@@ -1,24 +1,6 @@
 # Part of the Carbon Language project, under the Apache License v2.0 with LLVM
 # Exceptions. See /LICENSE for license information.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
-#
-# Installs Carbon to /usr/bin and /usr/lib/carbon.
-#
-# To install to /usr, run:
-#   bazel run -c opt //installers/local:install
-#
-# To use a custom install path, run:
-#   bazel run -c opt //installers/local:install
-#     --//installers/local:install_path=/my/path
-#
-# To uninstall, run:
-#   bazel //installers/local:uninstall
-#
-# The build mode is important for installs, as debug versions may be installed.
-# It is not relevant for uninstalls.
-#
-# If a custom install path is passed to :install, the same should be passed to
-# :uninstall.
 
 load("install.bzl", "install_path_rule")
 

installers/local/README.md

@@ -0,0 +1,40 @@
+# Local installer
+
+<!--
+Part of the Carbon Language project, under the Apache License v2.0 with LLVM
+Exceptions. See /LICENSE for license information.
+SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+-->
+
+This installs carbon-explorer locally for experimental use on Mac/Linux. It's
+not recommended for most users. Bear in mind that Carbon Language is
+**experimental** and still has no compiler. See
+[our project status](/README.md#project-status) for more information.
+
+To install to /usr, run:
+
+```shell
+bazel run -c opt //installers/local:install
+```
+
+To use a custom install path, run:
+
+```shell
+bazel run -c opt //installers/local:install \
+  --//installers/local:install_path=/my/path
+```
+
+To uninstall, run:
+
+```shell
+bazel //installers/local:uninstall
+```
+
+The build mode is important for installs, as debug versions may be installed. It
+is not relevant for uninstalls.
+
+If a custom install path is passed to :install, the same should be passed to
+:uninstall.
+
+Note this is just scripting paths: it's not intended to be a full-fledged
+install.