Add Geo rake task descriptions

To increase visibility of Geo rake tasks, add description so `rake -T`
shows them.

Closes gitlab-org/gitlab-ee#3366

changelogs/unreleased-ee/tc-geo-document-rake-tasks.yml

+---
+title: Add Geo rake task descriptions
+merge_request: 2925
+author:
+type: other

lib/tasks/geo.rake

@@ -2,14 +2,28 @@ task spec: ['geo:db:test:prepare']
 
 namespace :geo do
   namespace :db do |ns|
-    %i(drop create setup migrate rollback seed version reset).each do |task_name|
+    {
+      drop: 'Drops the Geo tracking database from config/database_geo.yml for the current RAILS_ENV.',
+      create: 'Creates the Geo tracking database from config/database_geo.yml for the current RAILS_ENV.',
+      setup: 'Create the Geo tracking database, load the schema, and initialize with the seed data.',
+      migrate: 'Migrate the Geo tracking database (options: VERSION=x, VERBOSE=false, SCOPE=blog).',
+      rollback: 'Rolls the schema back to the previous version (specify steps w/ STEP=n).',
+      seed: 'Load the seed data from db/geo/seeds.rb',
+      version: 'Retrieves the current schema version number.',
+      reset: 'Drops and recreates the database from db/geo/schema.rb for the current environment and loads the seeds.'
+    }.each do |task_name, task_desc|
+      desc task_desc
       task task_name do
         Rake::Task["db:#{task_name}"].invoke
       end
     end
 
     namespace :schema do
-      %i(load dump).each do |task_name|
+      {
+        load: 'Load a db/geo/schema.rb file into the database',
+        dump: 'Create a db/geo/schema.rb file that is portable against any DB supported by AR.'
+      }.each do |task_name, task_desc|
+        desc task_desc
         task task_name do
           Rake::Task["db:schema:#{task_name}"].invoke
         end
@@ -17,7 +31,12 @@ namespace :geo do
     end
 
     namespace :migrate do
-      %i(up down redo).each do |task_name|
+      {
+        up: 'Runs the "up" for a given migration VERSION.',
+        down: 'Runs the "down" for a given migration VERSION.',
+        redo: 'Rollbacks the database one migration and re migrate up (options: STEP=x, VERSION=x).'
+      }.each do |task_name, task_desc|
+        desc task_desc
         task task_name do
           Rake::Task["db:migrate:#{task_name}"].invoke
         end
@@ -25,6 +44,7 @@ namespace :geo do
     end
 
     namespace :test do
+      desc 'Check for pending migrations and load the test schema'
       task :prepare do
         Rake::Task['db:test:prepare'].invoke
       end