Add a note on pseudo-instructions

Signed-off-by: Miquel Sabaté Solà <mikisabate@gmail.com>

1 files changed, 22 insertions, 0 deletions

diff --git a/README.md b/README.md
index 8b6d5b8..5aff6a7 100644
--- a/README.md
+++ b/README.md
@@ -245,6 +245,28 @@ LDA #01     ; bad!
 lda #01     ; good!
 ```
 
+One good idea for `.macro` is to use them to define pseudo-instructions, as it's
+done in other assembly languages like RISC-V. For example, on [these scrolling
+examples](https://github.com/mssola/code.nes/tree/main/scroll) there is a macro
+for the pseudo-instruction `JAL`, which makes explicit when a `jmp` has been
+used instead of `jsr` for reducing the stack usage on tail calls. In this
+scenario, you can find code like this:
+
+```assembly
+.proc foo
+    ;; Previous code that might jump/branch to @end.
+
+    lda Some::Variable
+    bne @end
+    JAL prepare_next_column
+@end:
+    rts
+.endproc
+```
+
+Here the casing makes explicit that `JAL` is actually a pseudo-instruction, and
+so that it follows somewhat different rules than the ones by its side.
+
 ## Use the `@` prefix for named labels which affect the control flow
 
 Named labels which are part of the control flow are to use the `@` symbol as a