Add developer instructions to readme (#1252)

* Add developer instructions to readme

* Split dependencies by platform

* Remove unneeded packages

README.md

@@ -147,6 +147,31 @@ mosh-client packages to allow mosh-server usage without Perl.
 Notes for developers
 --------------------
 
+To start contributing to Mosh, install the following dependencies:
+
+Debian, Windows Subsystem for Linux:
+
+```
+$ sudo apt install -y build-essential protobuf-compiler \
+    libprotobuf-dev pkg-config libutempter-dev zlib1g-dev libncurses5-dev \
+    libssl-dev bash-completion tmux less
+```
+
+MacOS:
+
+```
+$ brew install protobuf automake
+```
+
+Once you have forked the repository, run the following to build and test Mosh:
+
+```
+$ ./autogen.sh
+$ ./configure
+$ make
+$ make check
+```
+
 Mosh supports producing code coverage reports by tests, but this feature is
 disabled by default. To enable it, make sure `lcov` is installed on your
 system. Then, configure and run tests: