Add markdown support in organization description (#13549)

Similarly to how you can write some markdown in user profile description, you can now use the same feature in organization description.
As discussed in discord.
kudos to @mrsdizzie and @zeripath 

visualization:
![image](https://user-images.githubusercontent.com/61180606/99115919-8004a200-25f3-11eb-8bbd-ab33de2cabb3.png)

templates/org/home.tmpl

@@ -13,7 +13,7 @@
 				</span>
 				{{if .IsOrganizationOwner}}<a class="middle text grey" href="{{.OrgLink}}/settings">{{svg "octicon-gear"}}</a>{{end}}
 			</div>
-			{{if .Org.Description}}<p class="desc">{{.Org.Description}}</p>{{end}}
+			{{if $.RenderedDescription}}<p class="render-content markdown">{{$.RenderedDescription|Str2html}}</p>{{end}}
 			<div class="text grey meta">
 				{{if .Org.Location}}<div class="item">{{svg "octicon-location"}} <span>{{.Org.Location}}</span></div>{{end}}
 				{{if .Org.Website}}<div class="item">{{svg "octicon-link"}} <a target="_blank" rel="noopener noreferrer" href="{{.Org.Website}}">{{.Org.Website}}</a></div>{{end}}