Add docs to all the roles

Change-Id: I8e7f93b00f5545e680c03fca622b29648f04e622
diff --git a/roles/ensure-cws-upload/README.md b/roles/ensure-cws-upload/README.md
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+Ensures that the [chrome-webstore-upload][1] program is installed.
+
+## Role variables
+- `version`: version of the chrome-webstore-upload program that must be
+installed. (default: `latest`)
+
+[1]: https://github.com/fregante/chrome-webstore-upload-cli
diff --git a/roles/ensure-genmanifest/README.md b/roles/ensure-genmanifest/README.md
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+Ensures that the [genmanifest program][1], which is part of the [webext][2] Go
+module, is installed. If Go 1.16 isn't installed, it also ensures that it is
+installed (in order to compile and install the program).
+
+## Role variables
+- `genmanifest_version`: version of the genmanifest program that must be
+installed. (default: `latest`)
+
+[1]: https://gerrit.avm99963.com/plugins/gitiles/gomodules/webext/+/refs/heads/master/genmanifest/
+[2]: https://gomodules.avm99963.com/webext/
diff --git a/roles/ensure-web-ext/README.md b/roles/ensure-web-ext/README.md
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+Ensures that Mozilla's [web-ext][1] program is installed. If NodeJS 14 isn't
+installed, it also ensures it is installed (in order to be able to run the
+program).
+
+It installs the latest web-ext version available.
+
+[1]: https://github.com/mozilla/web-ext
diff --git a/roles/fetch-cws-upload-log/README.md b/roles/fetch-cws-upload-log/README.md
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-Fetch the logs generated by the `cws-upload` role and store them in the
+Fetch the log generated by the `cws-upload` role and store them in the
 executor.
diff --git a/roles/fetch-web-ext-lint/README.md b/roles/fetch-web-ext-lint/README.md
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+Fetch the log generated by the `web-ext-lint` role and store them in the
+executor.
diff --git a/roles/web-ext-lint/README.md b/roles/web-ext-lint/README.md
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+Runs [`web-ext lint`][1] in order to lint a web extension and generate a report
+containing a list of warnings and errors that must be solved.
+
+## Role variables
+- `source_dir`: folder where the uncompressed extension files are located (if
+you use a tool –such as Webpack– to build your extension, this folder should
+have the compiled files which you would ZIP and upload to the extensions store.
+If this is a relative path, it is computed as if you were in the directory
+`{{ zuul.project.src_dir }}`. (default: `src`)
+- `extra_lint_flags`: flags that will be passed to the `web-ext lint` command,
+if specified.
+
+[1]: https://extensionworkshop.com/documentation/develop/web-ext-command-reference/#web-ext-lint