[fix] about.html: fix small inconsistencies in about page (#2219)

    It provides basic privacy by mixing your queries with searches on other

    platforms without storing search data. Queries are made using a POST request

    on every browser (except chrome*).  Therefore they show up in neither our

    logs, nor your url history.  In case of Chrome* users there is an exception,

    searx uses the search bar to perform GET requests.

    on every browser (except Chromium-based browsers*).  Therefore they show up 

    in neither our logs, nor your url history. In the case of Chromium-based

    browser users there is an exception: searx uses the search bar to perform GET

    requests.

    Searx can be added to your browser's search bar; moreover, it can be set as

    the default search engine.

  <ul>

    <li><a href="https://support.mozilla.org/en-US/kb/add-or-remove-search-engine-firefox">Firefox</a></li>

    <li><a href="https://support.microsoft.com/en-us/help/4028574/microsoft-edge-change-the-default-search-engine">Microsoft Edge</a></li>

    <li>Chrome based browsers <a href="https://www.chromium.org/tab-to-search">only add websites that the user navigates to without a path.</a>

    <li>Chromium-based browsers <a href="https://www.chromium.org/tab-to-search">only add websites that the user navigates to without a path.</a>

  </ul>

  <h2>Where to find anonymous usage statistics of this instance ?</h2>