Added image variable to chapter - now only one image is needed.

Modified chapter.html to use image stored in image variable as the hero image.
Added image to description on how to add a chapter in README.md.

Author: Tomasz-Kluczkowski

README.md

@@ -34,6 +34,8 @@ separating words with underscore (e.g. `london_pyton_sprints`).
 The content of the file has a header section with some fields (started and finished with
 ---), and the main description of the chapter afterwards. 
 We are using markdown files to store your data and they can contain either markdown tags for text formatting or pure html - it is up to you how to style your content.<br>
+The image that will represent your chapter should be in jpeg format. The size the content is optimized for is: 1920 x 600 px.
+Please name it <your_chapter_name_1920x600px.jpg>.
 This is the format:
 
     ---
@@ -42,6 +44,7 @@ This is the format:
     meetup_link: <url-of-your-other-website-if-any>
     address: "Description of your location, usually City, Country"
     country_code: <2-digit-country-code-used-for-the-flag>
+    image: <relative path to the chapter image>
     lat: <float-number-with-latitude-for-the-marker-in-the-map>
     lng: <float-number-with-longitude-for-the-marker-in-the-map>
     sponsors:
@@ -68,6 +71,7 @@ Example chapter setup
     meetup_link: https://www.meetup.com/Python-Sprints/
     address: London, United Kingdom
     country_code: gb
+    image: static/images/chapters/london_python_sprints_1920x600px.jpg
     lat: 51.512344
     lng: -0.090985
     sponsors:

_chapters/london_python_sprints.md

@@ -4,6 +4,7 @@ title: "London Python Sprints"
 meetup_link: https://www.meetup.com/Python-Sprints/
 address: London, United Kingdom
 country_code: gb
+image: static/images/chapters/london_python_sprints_1920x600px.jpg
 lat: 51.512344
 lng: -0.090985
 sponsors:

_layouts/chapter.html

@@ -6,21 +6,9 @@
         <main>
             <article>
                 <div class="chapter__background-img-container">
-                    <picture>
-                        <source srcset="../static/images/about/date-util-evening-session_480x150px.jpg 480w,
-                                ../static/images/about/date-util-evening-session_960x300px.jpg 960w,
-                                ../static/images/about/date-util-evening-session_1920x600px.jpg 1920w,
-                                ../static/images/about/date-util-evening-session_3840x1200px.jpg 3840w"
-                                media="(orientation: landscape)"
-                                sizes="100vw">
-                        <source srcset="../static/images/about/date-util-evening-session_750x650px.jpg 750w,
-                                ../static/images/about/date-util-evening-session_1650X1100px.jpg 1650w"
-                                media="(orientation: portrait)"
-                                sizes="100vw">
-                        <img class="chapter__background-img"
-                             src="../static/images/about/date-util-evening-session_960x300px.jpg"
-                             alt="About Us">
-                    </picture>
+                    <img class="chapter__background-img"
+                         src="{{ site.baseurl }}/{{ page.image }}"
+                         alt="{{ page.title }} photo">
                     <div class="chapter__page-title-container row container-fluid">
                         <div class="col-sm-12">
                             <h1 class="chapter__page-title">{{ page.title }}</h1>

_sass/chapter.scss

@@ -5,8 +5,12 @@
   }
 }
 
+
 .chapter__background-img {
-  @extend .page__background-img;
+  width: 100%;
+  height: 60vh;
+  object-fit: cover;
+  object-position: 50% 50%;
 }
 
 .chapter__page-title-container {