Add instructions for custom build

Custom-Build.md

@@ -0,0 +1,34 @@
+# Custom Build
+
+In order to build your own version of MultiMC, you need to create your own token and include it in the sources.
+
+This is done on the Azure portal through the following steps:
+
+
+1. Open Azure Active Directory on the portal.
+![](images/AzureToken1.png)
+
+2. Add a new App Registration
+![](images/AzureToken2.png)
+![](images/AzureToken3.png)
+
+3. Give it a name and set the supported account types to `Personal Microsoft accounts only`.
+![](images/AzureToken4.png)
+
+	1. If you were not able to set the account type as `Personal Microsoft accounts only`, go to the `Manifest` tab and change the line starting with `"signInAudience":` to `"signInAudience": "PersonalMicrosoftAccount",`. (If `accessTokenAcceptedVersion` is set to null, change it to `2`)
+
+4. Go to the Authentication tab.
+![](images/AzureToken5.png)
+
+5. Enable `Live SDK support` and `Allow public client flows`.
+![](images/AzureToken6.png)
+
+6. Go to the overview tab.
+![](images/AzureToken7.png)
+
+7. Copy the Application ID into the secrets.cpp file `MSAClientID` variable.
+![](images/AzureToken8.png)
+
+8. Rename the `notsecrets` folder to `secrets`.
+
+9. Build using the [instructions](https://github.com/MultiMC/Launcher/blob/develop/BUILD.md).

_Sidebar.md

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 * [[JSON Patches]]
 * [[Directory Structure]]
 * [[Custom Icons]]
+* [[Custom Build]]
 
 **External**