Added basic documentation.

README.md

@@ -1,7 +1,37 @@
 # Unsanitize Safelinks: A Utility for Microsoft's Safelinks
 
+Both the home and personal online offerings of Microsoft Outlook (e.g., Outlook.com, Office 365 Home,
+or Office 365 Personal) and the professional Office 365 offerings (e.g., as part of Office 365 Advanced
+Threat Detection) might rewrite links in received emails with the goal of protecting users against
+certain treats (e.g., phishing).
 
+For various reasons, one might to rewrite these `"safelinks" back into their original form. The script
+[unsantize-safelinks](./unsantize-safelinks) does exactly this. This can, for example, be used for
+displaying mails with mails nicely in [mutt](https://www.mutt.org). In your "muttrc" you need to 
+add/edit the following configuration:
 
+```muttrc
+set display_filter="unsanitize-safelinks"
+```
+
+If you want to also rewrite the links when using tools such as urlscan, use:
+
+```muttrc
+macro index,pager \cb "<pipe-message> unsanitize-safelinks| urlscan<Enter>"
+```
+
+And the following trick rewrites the links prior to editing a message (e.g., when replying):
+
+```muttrc
+set editor ="unsanitize-safelinks -i %s && $EDITOR %s"
+```
+
+Finally, if links should be rewritten when viewing the HTML-part, you need to edit your your ".mailcap"
+entry for type "text/html":
+
+```mailcap
+text/html; unsanitize-safelinks -i --html %s && /usr/bin/sensible-browser %s; description=HTML Text; nametemplate=%s.html
+```
 
 ## Author
 
@@ -15,6 +45,5 @@ SPDX-License-Identifier: BSD-2-Clause
 
 ## Master Repository
 
-The master git repository for this project is hosted 
+The master git repository for this project is hosted
 <https://git.logicalhacking.com/adbrucker/safelinks-tool>.
-