readme: Updates for installation and contributing

This is based on the discussion with Olof during a few different pull
requests.

Author: stffrdhrn

README.md

@@ -2,3 +2,46 @@ FuseSoC standard core library
 =============================
 
 This is the standard core library to be used with [FuseSoC](https://github.com/olofk/fusesoc)
+
+### Installation
+
+This library will be automatically cloned to `~/.local/share/fusesoc/fusesoc-cores`
+and added to `fusesoc.conf` when you run `fusesoc init`.
+
+If you have a existing FuseSoC setup and the above does not work for you,
+please consider this alternative installation method.  Use git to clone
+this repository and add it to your `fusesoc.conf`.  For example in
+`~/.config/fusesoc/fusesoc.conf`:
+
+```
+[main]
+cores_root =
+ /home/joe/work/fusesoc-cores
+cache_root = /home/joe/work/fuse-cache
+build_root = /home/joe/work/fuse-builds
+```
+
+### Contributing
+
+Cores for FuseSoC should follow the following guidelines.
+
+ - **No Code** Please do not store code in `fusesoc-cores`.  Please store
+   your code in a separate repo or somewhere it can be fetched with the
+   `url` provider.
+ - If your core is really small please consider storing in the
+   [tiny-cores](http://github.com/fusesoc/tiny-cores) repo.
+ - **Stay Modern** Use the modern sections in your core file like `fileset`
+   and `parameter`, please no obsolete `verilog` sections.  For details on
+   migrating old cores to the current standard please refer to the
+   [FuseSoC migration guide](https://github.com/olofk/fusesoc/blob/master/doc/migrations.adoc).
+ - **Versioning** Each core should be versioned with either
+   - **Versioned** For cores where the upstream provider provides a release
+     version, in git using tags is ideal, please use the corresponding
+     release version.
+   - **Pseudo-versioned** When an core's upstream provider is out of your
+     control and does not use versions please use version `0` and point to
+     a location which is unique for that revision (e.g. the sha for git
+     repos or revision for svn repos instead of pointing to master, which
+     might change over time).  If you need to refer to a newer version of
+     the upstream repo, still without a proper version, step the revision
+     number (`0-r1`, `0-r2`..etc).