The module .info file

Here is the original D7 optimizely.info file.

name = Optimizely
description = Manages loading Optimizely generated
    project javascript file(s) to enable A/B testing.
core = 7.x
php = 5.2
project = "optimizely"
configure = admin/config/system/optimizely/settings
files[] = optimizely.test

In Drupal 8 the required .info file for a module has been replaced with a  .info.yml  file, which serves the same purpose. The new syntax is YAML, which is more generally known and accepted.

Here is the very first cut for such a file. These three keys seem to be the minimum required for D8 to recognize the presence of a module.

name: Optimizely
type: module
core: 8.x

Contrib and custom modules may now be placed in the top-level  modules  directory (whereas core modules are placed in  core/modules ). Subdirectories may be used. So I created this new file in the path

modules/custom/optimizely/optimizely.info.yml

Here's a fleshed out version which is equivalent to the original (as far as I know at this point).

# These first three properties are required.
name: Optimizely
type: module
core: 8.x

# This value for the description key is broken across
# multiple lines to demonstrate how it's done and for
# better formatting in this blog.
description: >
  Manages loading Optimizely generated project
  javascript file(s) to enable A/B testing.

php: 5.2
project: optimizely

# The configure property specifies a "route name",
# which I will define later.
configure: optimizely.settings

# files[] are no longer needed because of autoloading

The path to the configuration menu is replaced by use of the new routing system, which I will be learning and getting into later.

From https://drupal.org/node/1935708: "Remove any files[] entries. Classes are now autoloaded using a separate mechanism".

Syntax Notes: 

• You must put one or more spaces or tabs after each colon.
• Quote marks are optional around string values.
• Comments start with a pound sign #
• Indentation is syntactically significant and indicates elements at the same level.
• I broke up the value for the description property into two lines by (1) using a > character which means the newlines are to be folded and (2) indenting the lines of the string value.

Sources:

.info files are now .info.yml files
https://drupal.org/node/1935708
Includes a couple of examples on the new .info.yml files.

YAML
https://en.wikipedia.org/wiki/YAML
Description and tutorial for YAML syntax, data types, et al. Has technical details if you want to delve into them but the first part of the article is a good intro.