Add Add new project section to the readme

Credits go to @olafurpg for his comment in scala/scala3#2182

Author: allanrenucci

README.md

@@ -1,11 +1,30 @@
 # Dotty Community Build
 [![Community Build Status](https://travis-ci.org/lampepfl/dotty-community-build.svg?branch=master)](https://travis-ci.org/lampepfl/dotty-community-build)
 
-
 This repository contains tests to build a corpus of Scala open sources projects
 against the latest changes in Dotty.
 
 To run the community build on a local machine, clone the repo and execute `./run.sh`.
 
 The tests will by default run against the latest NIGHTLY build of dotty.
 To customize the dotty version, set the environment variable `export DOTTY_VERSION=X.Y.Z`.
+
+## Adding a new project
+To add a new project `ORG/REPO` to the community build you can follow this steps:
+1. Fork `ORG/REPO` to `dotty-staging/REPO`
+2. Clone `dotty-staging/REPO`, create a branch `dotty` and push the `dotty` branch 
+3. Open `dotty-staging/REPO` on Github. Go to `Settings > Branches`. Change the default branch to `dotty`
+4. Go to https://travis-ci.org/profile/dotty-staging and enable that repo. You may need to click on `Sync account` and
+   reload to see the newly forked repo
+5. Fork the `dotty-staging/REPO` to your personal github account
+6. Edit the build to use `sbt-dotty` and fix all the compilation errors. Example PRs:
+    - https://github.com/dotty-staging/scalacheck/pull/1
+    - https://github.com/dotty-staging/squants/pull/1
+    - https://github.com/dotty-staging/algebra/pull/1
+7. Once the project complies with dotty, copy the `.travis.yml` file from
+   [here](https://github.com/dotty-staging/squants/blob/37ea54761b5e80ddc0dfc273fc4bbad430f201f5/.travis.yml#L3)
+   and adjust the compile task. I'm only compiling projects for now, not running any tests.
+   Just making sure that the projects compiles is a great start
+8. Open PR to merge your changes into the `dotty` branch of hte `dotty-staging/REPO`
+9. Once PR is merged into `dotty-staging/REPO`, open a PR to `lampepfl/dotty-community-build` adding the new
+   `dotty-staging/REPO` to the community build. Example PR: https://github.com/lampepfl/dotty-community-build/pull/3