[Docs] Document the company-mode setup

doc/modules/company.md

@@ -0,0 +1,28 @@
+# Prelude Company
+
+!!! Note
+
+    This module is enabled by default.
+
+[company](https://company-mode.github.io/) is a completion library.
+
+This module simply provides some reasonable defaults for it and enables `company-mode`:
+
+```
+(setq company-idle-delay 0.5)
+(setq company-show-numbers t)
+(setq company-tooltip-limit 10)
+(setq company-minimum-prefix-length 2)
+(setq company-tooltip-align-annotations t)
+;; invert the navigation direction if the the completion popup-isearch-match
+;; is displayed on top (happens near the bottom of windows)
+(setq company-tooltip-flip-when-above t)
+
+(global-company-mode 1)
+```
+
+You can adjust the configuration further in your personal config.
+
+`company-mode` has [many extensions](https://github.com/company-mode/company-mode/wiki/Third-Party-Packages)
+for various programming languages.
+Some of Prelude's modules will install and enable the relevant extensions when necessary.

doc/modules/index.md

@@ -83,7 +83,7 @@ The following programming languages have enhanced support in Prelude:
 
 ## Other Modules
 
-- company
+- [Company](company.md)
 - [ERC](erc.md)
 - evil
 - helm

mkdocs.yml

@@ -9,6 +9,7 @@ pages:
 - Configuration: configuration.md
 - Modules:
     - Overview: modules/index.md
+    - Company: modules/company.md
     - ERC: modules/erc.md
     - Programming: modules/programming.md
     - Python: modules/python.md