docs: created 2.10 migration guide

Author: Grubba27

guide/source/2.10-migration.md

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+---
+title: Migrating to Meteor 2.10
+description: How to migrate your application to Meteor 2.10.
+---
+
+Most of the new features in Meteor 2.10 are either applied directly behind the scenes (in a backwards compatible manner) or are opt-in. For a complete breakdown of the changes, please refer to the [changelog](http://docs.meteor.com/changelog.html).
+
+The above being said, there are a few items that you should implement to have easier time in the future.
+
+<h3 id="async-tracker">Async Tracker</h3>
+
+Wrapping your async calls in a ```Tracker.withComputation``` method will make sure that even async calls are reactive.
+
+before if you used a code like the one below it would only run once and would not be reactive
+```javascript
+Tracker.autorun(async function example1() {
+  let asyncData = await asyncDataFunction();
+  let users = Meteor.users.find({}).fetch();
+});
+```
+To be reactive before 2.10 you would need to call the reactive data sources before the async call
+
+```javascript
+Tracker.autorun(async function example2() {
+  let users = Meteor.users.find({}).fetch();
+  let asyncData = await asyncDataFunction();
+});
+```
+Now you can have both examples reactive by wrapping the async call in a ```Tracker.withComputation``` method
+
+```javascript
+
+Tracker.autorun(async function example1(computation) {
+  let asyncData = await Tracker.withComputation(computation, () => asyncDataFunction());
+  let users = Meteor.users.find({}).fetch();
+});
+
+Tracker.autorun(async function example2(computation) {
+  let users = await Tracker.withComputation(computation, () => Meteor.users.find({}).fetch());
+  let asyncData = await Tracker.withComputation(computation, () => asyncDataFunction());
+  
+});
+
+// using async mongo api
+Tracker.autorun(async function example2(computation) {
+  let asyncData = await Tracker.withComputation(computation, () => asyncDataFunction());
+  let users = await Tracker.withComputation(computation, () => Meteor.users.find({}).fetchAsync());
+});
+```
+<h2 id="older-versions">Migrating from a version older than 2.9?</h2>
+
+If you're migrating from a version of Meteor older than Meteor 2.9, there may be important considerations not listed in this guide. Please review the older migration guides for details:
+
+* [Migrating to Meteor 2.9](2.9-migration.html) (from 2.8)
+* [Migrating to Meteor 2.8](2.8-migration.html) (from 2.7)
+* [Migrating to Meteor 2.7](2.7-migration.html) (from 2.6)
+* [Migrating to Meteor 2.6](2.6-migration.html) (from 2.5)
+* [Migrating to Meteor 2.5](2.5-migration.html) (from 2.4)
+* [Migrating to Meteor 2.4](2.4-migration.html) (from 2.3)
+* [Migrating to Meteor 2.3](2.3-migration.html) (from 2.2)
+* [Migrating to Meteor 2.2](2.2-migration.html) (from 2.0)
+* [Migrating to Meteor 2.0](2.0-migration.html) (from 1.12)
+* [Migrating to Meteor 1.12](1.12-migration.html) (from 1.11)
+* [Migrating to Meteor 1.11](1.11-migration.html) (from 1.10.2)
+* [Migrating to Meteor 1.10.2](1.10.2-migration.html) (from 1.10)
+* [Migrating to Meteor 1.10](1.10-migration.html) (from 1.9.3)
+* [Migrating to Meteor 1.9.3](1.9.3-migration.html) (from 1.9)
+* [Migrating to Meteor 1.9](1.9-migration.html) (from 1.8.3)
+* [Migrating to Meteor 1.8.3](1.8.3-migration.html) (from 1.8.2)
+* [Migrating to Meteor 1.8.2](1.8.2-migration.html) (from 1.8)
+* [Migrating to Meteor 1.8](1.8-migration.html) (from 1.7)
+* [Migrating to Meteor 1.7](1.7-migration.html) (from 1.6)
+* [Migrating to Meteor 1.6](1.6-migration.html) (from 1.5)
+* [Migrating to Meteor 1.5](1.5-migration.html) (from 1.4)
+* [Migrating to Meteor 1.4](1.4-migration.html) (from 1.3)
+* [Migrating to Meteor 1.3](1.3-migration.html) (from 1.2)