add localmode docs

Author: krzkaczor

README.md

@@ -36,5 +36,6 @@ Expect more docs soon...
    1. Testing checks
 1. [How to build X?](how-to-build-X.md)
 1. [Client API reference](client-api.md)
+1. [Localmode](localmode.md)
 1. [FAQ](faq.md)
 1. [Roadmap](roadmap.md)

localmode.md

@@ -0,0 +1,11 @@
+# Local mode
+
+Local mode enables you to simulate codechecks running on your local machine.
+
+To use it just run `codechecks` CLI on local machine. If you want to explicitly provide project slug
+use `--project` option ex. `codechecks --project krzkaczor/ts-essentials`.
+
+It will try to get all required information from GIT repository like project slug (based on remote
+config), changed files etc. Codechecks API for public repos is read only without any auth so you can
+access baselines. Any reports will be rendered in console. It will always simulate PR to master
+branch.