Modify README to be more readable

CONTRIBUTING.md

@@ -0,0 +1,50 @@
+# Documentation
+Dokka is added to the project, so to create (or, better say, update) the docs, you need to run
+```
+./gradlew charts:dokkaHtml
+```
+on the root dir of the project.
+
+After the task is done, copy the generated docs into `./docs`, which can also be done by running
+```
+rm -rf ./docs ; cp -r ./charts/build/dokka/html ./docs
+```
+
+# Testing
+Testing is implemented using [Shot](https://github.com/pedrovgs/Shot) library. In order to run
+it against prerecorded results, create at least one of the following emulators:
+- tablet: Nexus 10, running API 31
+- phone: Pixel 4a, running API 31
+
+For tests to work, make sure you create emulators with default values, as **screen size and
+density must be exactly the same**.
+
+Details as to how to run the tests are in the link to the library itself, but to run it against
+prerecorded screenshots, run the following command:
+```
+./gradlew executeScreenshotTests -PdirectorySuffix=$deviceName
+```
+where `$deviceName` is one of:
+- Nexus_10_API_31
+- Pixel_4a_API_31
+
+## Flakiness
+Due to differences in graphics between M1 and x86 chips, images appear different to the script
+and so the tests fail (difference between images can be well above 10%). To human eye they do
+seem the same, though. This is explained and shown in [issue 265](https://github.com/pedrovgs/Shot/issues/265). Until this is fixed, there is a way to test stuff at least locally:
+
+1. uncomment tests that are commented out because of this issue
+2. record all the tests
+3. make the desired changes in the code
+4. check the new UI state against the pre-recorded screenshots (I suggest removing tolerance if
+   the tests were recorded on your machine!)
+5. comment the flaky tests out again
+6. revert the screenshots
+
+## Other issues
+
+- Library [does not work with Java 17](https://github.com/pedrovgs/Shot/pull/292). The error
+  itself is not as obvious as one might expect, though. To fix the issue, use Java 11.
+- Java heap space sometimes [needs to be enlarged](https://github.com/pedrovgs/Shot/issues/304)
+- You might encounter [INSTALL_FAILED_SHARED_USER_INCOMPATIBLE](https://stackoverflow.com/questions/15205159/install-failed-shared-user-incompatible-while-using-shared-user-id)
+  issue. [Here](https://stackoverflow.com/a/21809883/6835732) is a shortcut to the answer.