Merge branch 'improve-readability' into 'master'

Set max-width for README, issue and merge request description

It allows easier text reading on big screens

### Problem

Text is hard to read on wide screens:

![Screenshot_2015-08-14_11.33.39](https://gitlab.com/gitlab-org/gitlab-ce/uploads/2bdb092c09495c7aa94b0589df4b7e65/Screenshot_2015-08-14_11.33.39.png)

### Solution

Set max-width to content. Screenshots:

![Screenshot_2015-08-14_11.31.54](https://gitlab.com/gitlab-org/gitlab-ce/uploads/00cd7a77b81b30458a1675ec562d7463/Screenshot_2015-08-14_11.31.54.png)
![Screenshot_2015-08-14_10.53.16](https://gitlab.com/gitlab-org/gitlab-ce/uploads/4756f87a3bbb7179e55b1c8f8ee40459/Screenshot_2015-08-14_10.53.16.png)
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

See merge request !1161

CHANGELOG

@@ -55,6 +55,7 @@ v 7.14.0 (unreleased)
   - Add a label for merged branches on branches page (Florent Baldino)
   - Detect .mkd and .mkdn files as markdown (Ben Boeckel)
   - Fix: User search feature in admin area does not respect filters
+  - Set max-width for README, issue and merge request description for easier read on big screens
 
 v 7.13.5
   - Satellites reverted

app/assets/stylesheets/base/variables.scss

@@ -13,6 +13,7 @@ $code_line_height: 1.5;
 $border-color: #E5E5E5;
 $background-color: #f5f5f5;
 $header-height: 50px;
+$readable-width: 1100px;
 
 
 /*

app/assets/stylesheets/pages/issuable.scss

@@ -45,3 +45,9 @@
 
   .btn { font-size: 13px; }
 }
+
+.issuable-details {
+  .description {
+    max-width: $readable-width;
+  }
+}

app/assets/stylesheets/pages/tree.scss

@@ -116,6 +116,9 @@
 }
 
 .readme-holder {
+  margin: 0 auto;
+  max-width: $readable-width;
+
   .readme-file-title {
     font-size: 14px;
     font-weight: bold;