Merge pull request #824 from unoplatform/dev/jela/doc-initialmemory

docs: Clarify initial_memory

Author: jeromelaban

doc/runtime-execution-modes.md

@@ -147,6 +147,24 @@ In order to determine which methods are still using the interpreter, you can use
 
 The logs from the AOT compiler can be found in [binlogs generated](https://aka.platform.uno/msbuild-troubleshoot) from the build.
 
+### Increasing the Initial Memory Size
+
+When building with Mixed AOT/Interpreter modes, the initial memory may need to be adjusted in the project configuration if the following error message appears:
+
+```
+wasm-ld: error: initial memory too small, 17999248 bytes needed
+```
+
+In order to fix this, you'll need to set the [`INITIAL_MEMORY`](https://emscripten.org/docs/tools_reference/settings_reference.html?highlight=initial_memory#initial-memory) emscripten parameter, this way:
+
+```xml
+<ItemGroup>
+  <WasmShellExtraEmccFlags Include="-s INITIAL_MEMORY=64MB" />
+</ItemGroup>
+```
+
+which will set the initial memory size accordingly. Note that setting this value to a sufficiently large value (based on your app's usual memory consumption) can improve the startup performance.
+
 ## Required configuration for AOT, Mixed Mode or external bitcode support compilation on Windows 10
 
 ### Native windows tooling