add Gemfile with jekyll dependencies

Signed-off-by: Jakub Sokołowski <jakub@status.im>

Gemfile

@@ -0,0 +1,4 @@
+source "https://rubygems.org"
+
+gem "just-the-docs"
+gem "kramdown-parser-gfm"

Gemfile.lock

@@ -0,0 +1,75 @@
+GEM
+  remote: https://rubygems.org/
+  specs:
+    addressable (2.8.0)
+      public_suffix (>= 2.0.2, < 5.0)
+    colorator (1.1.0)
+    concurrent-ruby (1.1.9)
+    em-websocket (0.5.2)
+      eventmachine (>= 0.12.9)
+      http_parser.rb (~> 0.6.0)
+    eventmachine (1.2.7)
+    ffi (1.15.4)
+    forwardable-extended (2.6.0)
+    http_parser.rb (0.6.0)
+    i18n (1.8.10)
+      concurrent-ruby (~> 1.0)
+    jekyll (4.2.0)
+      addressable (~> 2.4)
+      colorator (~> 1.0)
+      em-websocket (~> 0.5)
+      i18n (~> 1.0)
+      jekyll-sass-converter (~> 2.0)
+      jekyll-watch (~> 2.0)
+      kramdown (~> 2.3)
+      kramdown-parser-gfm (~> 1.0)
+      liquid (~> 4.0)
+      mercenary (~> 0.4.0)
+      pathutil (~> 0.9)
+      rouge (~> 3.0)
+      safe_yaml (~> 1.0)
+      terminal-table (~> 2.0)
+    jekyll-sass-converter (2.1.0)
+      sassc (> 2.0.1, < 3.0)
+    jekyll-seo-tag (2.7.1)
+      jekyll (>= 3.8, < 5.0)
+    jekyll-watch (2.2.1)
+      listen (~> 3.0)
+    just-the-docs (0.3.3)
+      jekyll (>= 3.8.5)
+      jekyll-seo-tag (~> 2.0)
+      rake (>= 12.3.1, < 13.1.0)
+    kramdown (2.3.1)
+      rexml
+    kramdown-parser-gfm (1.1.0)
+      kramdown (~> 2.0)
+    liquid (4.0.3)
+    listen (3.6.0)
+      rb-fsevent (~> 0.10, >= 0.10.3)
+      rb-inotify (~> 0.9, >= 0.9.10)
+    mercenary (0.4.0)
+    pathutil (0.16.2)
+      forwardable-extended (~> 2.6)
+    public_suffix (4.0.6)
+    rake (13.0.1)
+    rb-fsevent (0.11.0)
+    rb-inotify (0.10.1)
+      ffi (~> 1.0)
+    rexml (3.2.5)
+    rouge (3.26.0)
+    safe_yaml (1.0.5)
+    sassc (2.4.0)
+      ffi (~> 1.9)
+    terminal-table (2.0.0)
+      unicode-display_width (~> 1.1, >= 1.1.1)
+    unicode-display_width (1.7.0)
+
+PLATFORMS
+  ruby
+
+DEPENDENCIES
+  just-the-docs
+  kramdown-parser-gfm
+
+BUNDLED WITH
+   2.1.4