[debugger] Update breakpoint documentation.

The "@main" syntax is no longer necessary for Rust so references to this
are removed and the namespace searching behavior is documented.

Change-Id: Ib0ab76297f2088daf3445f48adc1cca500d7a0b8
diff --git a/docs/development/debugger/debugger_usage.md b/docs/development/debugger/debugger_usage.md
index 9588ed0..56c2512e 100644
--- a/docs/development/debugger/debugger_usage.md
+++ b/docs/development/debugger/debugger_usage.md
@@ -40,9 +40,8 @@
 > truncated. If the filter isn't working, check the actual name in "ps". We hope
 > to have a better way to match this in the future.
 
-This example sets a pending breakpoint on `main` (Rust users: use "@main") to
-stop at the beginning of execution, and waits for a process called "my_app" to
-start:
+This example sets a pending breakpoint on `main` to stop at the beginning of
+execution, and waits for a process called "my_app" to start:
 
 ```
 [zxdb] attach my_app
@@ -100,17 +99,13 @@
 within the debugger which avoids the "attach" dance:
 
 ```
-[zxdb] break @main
+[zxdb] break main
 Breakpoint 1 (Software) on Global, Enabled, stop=All, @ @main
 Pending: No matches for location, it will be pending library loads.
 
 [zxdb] run /bin/cowsay
 ```
 
-> The "@main" symbol will match the process' entrypoint which is particularly
-> useful for Rust where things live in a namespace. For C/C++, it's equivalent
-> to "main".
-
 If you get a shared library load error or errors about files or services not
 being found, it means the app can't be run from within the debugger's launcher
 environment. This is true even for things that may seem relatively simple.
@@ -406,23 +401,18 @@
 
 A location can be expressed in many different ways.
 
-  * Plain function name:
+  * Plain function name. This will match functions with the name in any
+    namespace:
 
     ```
     break main
     ```
 
-    There is a special symbol "@main" that matches the entrypoint of the process.
-    This is useful for Rust where the entrypoint is usually in a namespace:
-
-    ```
-    break @main
-    ```
-
-  * Member function or functions inside namespaces:
+  * Member function or functions inside a specific namespace or class:
 
     ```
     break my_namespace::MyClass::MyFunction
+    break ::OtherFunction
     ```
 
   * Source file + line number (separate with a colon):