Adding contrib document

CONTRIBUTING.md

@@ -0,0 +1,107 @@
+# Contributing Guidelines
+
+This document is inspired by similar instructions document in the GDAL and pygmt repositories. 
+
+These are some of the many ways to contribute to the ISCE project:
+
+* Submitting bug reports and feature requests
+* Writing tutorials or jupyter-notebooks
+* Fixing typos, code and improving documentation
+* Writing code for everyone to use
+
+If you get stuck at any point you can create an issue on GitHub (look for the *Issues*
+tab in the repository) or contact us on the [user forum](http://earthdef.caltech.edu/projects/isce_forum/boards).
+
+For more information on contributing to open source projects,
+[GitHub's own guide](https://guides.github.com/activities/contributing-to-open-source/)
+is a great starting point if you are new to version control.
+
+
+## Ground Rules
+
+We realize that we don't have a Continuous Integration (CI) system in place yet (maybe you could start by contributing this). So, please be patient if Pull Requests result in some detailed discussions.  
+
+## Git workflows with ISCE
+
+This is not a git tutorial or reference manual by any means. This just collects a few best practice for git usage for ISCE development. There are plenty of good resources on YouTube and online to help get started.
+
+### Commit message
+
+Indicate a component name, a short description and when relevant, a reference to a issue (with 'fixes #' if it actually fixes it)
+
+```
+COMPONENT_NAME: fix bla bla (fixes #1234)
+
+Details here...
+```
+
+### Initiate your work repository
+
+
+Fork isce-framework/isce from github UI, and then
+```
+git clone https://github.com/isce_framework/isce2
+cd isce2
+git remote add my_user_name https://github.com/my_user_name/isce2.git
+```
+
+### Updating your local master against upstream master
+
+```
+git checkout master
+git fetch origin
+# Be careful: this will loose all local changes you might have done now
+git reset --hard origin/master
+```
+
+### Working with a feature branch
+
+```
+git checkout master
+(potentially update your local master against upstream, as described above)
+git checkout -b my_new_feature_branch
+
+# do work. For example:
+git add my_new_file
+git add my_modifid_message
+git rm old_file
+git commit -a 
+
+# you may need to resynchronize against master if you need some bugfix
+# or new capability that has been added to master since you created your
+# branch
+git fetch origin
+git rebase origin/master
+
+# At end of your work, make sure history is reasonable by folding non
+# significant commits into a consistent set
+git rebase -i master (use 'fixup' for example to merge several commits together,
+and 'reword' to modify commit messages)
+
+# or alternatively, in case there is a big number of commits and marking
+# all them as 'fixup' is tedious
+git fetch origin
+git rebase origin/master
+git reset --soft origin/master
+git commit -a -m "Put here the synthetic commit message"
+
+# push your branch
+git push my_user_name my_new_feature_branch
+From GitHub UI, issue a pull request
+```
+
+If the pull request discussion results in changes,
+commit locally and push. To get a reasonable history, you may need to
+```
+git rebase -i master
+```
+, in which case you will have to force-push your branch with 
+```
+git push -f my_user_name my_new_feature_branch
+```
+
+### Things you should NOT do
+
+(For anyone with push rights to github.com/isce-framework/isce2) Never modify a commit or
+the history of anything that has been
+committed to https://github.com/isce-framework/isce2