doc: merge all sharing methods under a single "Sharing content" page

 * formatting, wording, reordering, general improvements
 * move blog/pastebin/notepad item from index.md to this page
 * add TODOs
 * add the new page to mkdocs TOC

Part of https://github.com/shaarli/Shaarli/issues/598

1 files changed, 88 insertions, 0 deletions

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+Content posted to Shaarli is separated in items called _Shaares_. For each Shaare, 
+you can customize the following aspects:
+
+ * URL to link to
+ * Title
+ * Free-text description
+ * Tags
+ * Public/private status
+
+--------------------------------------------------------------------------------
+
+## Adding new Shaares
+
+While logged in to your Shaarli, you can add new Shaares in several ways:
+
+ * [+Shaare button]
+ * [Bookmarklet]
+ * [Firefox Share](#firefox-share)
+ * Third-party [apps and browser addons](Community-\&-Related-software.md#mobile-apps)
+
+
+### +Shaare button
+
+ * While logged in to your Shaarli, click the **`+Shaare`** button located in the toolbar.
+ * Enter the URL of a link you want to share.
+ * Click `Add link`
+ * The `New Shaare` dialog appears, allowing you to fill in the details of your Shaare.
+   * The Description, Title, and Tags will help you find your Shaare later using tags or full-text search.
+   * You can also check the “Private” box so that the link is saved but only visible to you (the logged-in user).
+ * Click `Save`.
+
+<!-- TODO Add screenshot of add/edit link dialog -->
+
+### Bookmarklet
+
+The _Bookmarklet_ \[[1](https://en.wikipedia.org/wiki/Bookmarklet)\] is a special 
+browser bookmark you can use to add new content to your Shaarli. This bookmarklet is 
+compatible with Firefox, Opera, Chrome and Safari. To set it up:
+
+ * Access the `Tools` page from the button in the toolbar.
+ * Drag the **`✚Shaare link` button** to your browser's bookmarks bar.
+
+Once this is done, you can shaare any URL you are visiting simply by clicking the 
+bookmarklet in your browser! The same `New Shaare` dialog as above is displayed.
+
+| Note | Websites which enforce Content Security Policy (CSP), such as github.com, disallow usage of bookmarklets. Unfortunately, there is nothing Shaarli can do about it. \[[1](https://github.com/shaarli/Shaarli/issues/196)]\ \[[2](https://bugzilla.mozilla.org/show_bug.cgi?id=866522)]\ \[[3](https://code.google.com/p/chromium/issues/detail?id=233903)]\ |
+|---------|---------|
+
+| Note | Under Opera, you can't drag'n drop the button: You have to right-click on it and add a bookmark to your personal toolbar. |
+|---------|---------|
+
+![](images/bookmarklet.png)
+
+
+### Firefox Share
+
+Before using Firefox Share, you must first add Shaarli as a sharing provider:
+
+- Click the `Tools` button in the top bar
+- Click the `✚Add to Firefox social` button and accept the activation.
+
+Once this is done, you can share any URL you are visiting by clicking the Firefox 
+_Share_ button [images/firefoxshare.png](images/firefoxshare.png)
+
+| Note | Firefox Share is no longer available for Firefox 57 and later versions. |
+|---------|---------|
+
+| Note | Your Shaarli instance must be hosted on an HTTPS (SSL/TLS secure connection) enabled server for Firefox Share to work. Firefox Share will not work over plaintext HTTP connections. |
+|---------|---------|
+
+--------------------------------------------------------------------------------
+
+## Editing Shaares
+
+Any Shaare can edited by clicking its ![](https://raw.githubusercontent.com/shaarli/Shaarli/master/images/edit_icon.png) `Edit` button.
+
+Editing a Shaare will not change it's permalink, each permalink always points to the 
+latest revision of a Shaare.
+
+--------------------------------------------------------------------------------
+
+## Using shaarli as a blog, notepad, pastebin...
+
+While adding or editing a link, leave the URL field blank to create a text-only 
+("note") post. This allows you to post any kind of text content, such as blog 
+articles, private or public notes, snippets... There is no character limit! You can 
+access your Shaare from its permalink.
+