Merge 'docs: migrate the docs from the scylla-docs repo' from Anna St…

…uchlik

This PR migrates the ScyllaDB end-user documentation from the [scylla-docs](https://github.com/scylladb/scylla-docs/) repository, according to the [migration plan](https://docs.google.com/document/d/15yBf39j15hgUVvjeuGR4MCbYeArqZrO1ir-z_1Urc6A/edit?usp=sharing). All the files are added to the `docs` subfolder.

 **This PR does not cover any content changes.**

How to test this PR:

1. Go to `scylla/docs`.
2. Run `make preview`. The docs should build without any warnings.
3. Open http://127.0.0.1:5500/ in your browser. You should see the documentation landing page:
![image](https://user-images.githubusercontent.com/37244380/177358869-af9f1b78-e528-4d0d-9479-cc69e25f3b67.png)

Closes #10976

* github.com:scylladb/scylla:
  doc: fix errors -fix the indent in the conf.py file
  doc: fix the path to Alternator
  doc: fix errors - add Alternator to the toctree
  doc: fix errors- update the conf.py file
  doc: fix errors - remove the CNAME file
  doc: add the CNAME and robots files
  doc: move index and README from scylla-docs repo
  doc: move the documentation from the scylla-docs repo
  doc: remove the old index file

docs/README.md

@@ -0,0 +1,113 @@
+# Scylla documentation
+
+This is the repository for [Scylla documentation site](http://docs.scylladb.com/)
+
+To report an issue with the documentation, please use GitHub issues.
+
+This repository accepts GitHub pull requests.
+
+**Send pull requests to the master branch, not gh-pages.  gh-pages will be overwritten by deploy without warning.**
+
+
+## Prerequisites
+
+* Python 3. Check your version with `$ python --version`
+* Vale CLI (optional to lint docs). [Install Vale](https://docs.errata.ai/vale/install) for your operative system.
+
+### Prerequisites: Mac OS X
+
+You must have a working [Homebrew](http://brew.sh/) in order to install the needed tools.
+
+You also need the standard utility `make`.  (I don't know if this comes with Mac OS X.)
+
+Check if you have these two items with
+
+```sh
+brew help
+make -h
+```
+
+### Prerequisites: Fedora 29/Debian-based Linux Distributions
+
+This should work out of the box with Fedora 29.
+
+### Prerequisites: Windows
+
+Use "Bash on Ubuntu on Windows", everything should be same as on a debian-based Linux.
+Note: livereload seems not working on Windows.
+
+## Prerequisites: other systems
+
+FIXME
+
+# Working on the docs
+
+Work on a task branch and send pull requests for
+master.  Master is the default branch.
+
+Run `make preview` to make the docs and preview locally.
+
+
+# Deploy
+
+If you have the rights to push to the live site, run `make deploy` to deploy.
+
+# Lint
+
+Lint all:
+
+```sh
+make proofread
+```
+
+Lint one file (e.g. README.md):
+
+```sh
+make proofread path=README.md
+```
+
+Lint one folder (e.g. getting-started):
+
+```sh
+make proofread path=getting-started
+```
+
+# Cleanup
+
+You can clean up all the build products and auto-installed Python stuff with:
+
+```sh
+make pristine
+```
+
+# Contributor info
+
+If you are interested in contributing to Scylla
+docs, please read the Scylla open source page at
+http://www.scylladb.com/opensource/ and complete
+a Scylla contributor agreement if needed.  We can
+only accept documentation pull requests if we have
+a contributor agreement on file for you
+
+# Submitting a KB Article
+
+If you are submitting a Knowledgebase Article (KBA), use the following guidelines:
+* In the `/kb_common` directory there is a template for KBAs. It is called `kb-article-template.rst`.
+* Make a copy of this file in the `/kb directory`, saving it with a unique name.
+* Open the template and fill in the required inforation. 
+* Remove what is not needed. 
+* Run`make preview` to make the docs and preview locally.
+* Send a PR - add KBA in the title. 
+
+# Third-party documentation
+
+ * Do any copying as a separate commit.  Always commit an unmodified version first and then do any editing in a separate commit.
+
+ * We already have a copy of the Apache license in our tree so you do not need to commit a copy of the license.
+
+ * Include the copyright header from the source file in the edited version.  If you are copying an Apache Cassandra document with no copyright header, use:
+
+```
+This document includes material from Apache Cassandra.
+Apache Cassandra is Copyright 2009-2014 The Apache Software Foundation.
+```