Add tips to README

README.md

@@ -2,3 +2,53 @@ libkernaux
 ==========
 
 Auxiliary library for kernel development.
+
+
+
+Tips
+----
+
+Configure with cross-compiler in `$PATH` to make without it in `$PATH`:
+
+```
+./configure \
+  --host=i686-elf \
+  AR="$(which i686-elf-ar)" \
+  CC="$(which i686-elf-gcc)" \
+  RANLIB="$(which i686-elf-ranlib)" \
+  CFLAGS='-std=gnu99 -ffreestanding -nostdinc -nostdlib -fno-builtin -fno-stack-protector -Wall -Wextra'
+```
+
+Check if compilation targets i386: `objdump -d src/arch/i386.o`.
+
+It should output something like this:
+
+```
+src/arch/i386.o:     file format elf32-i386
+
+
+Disassembly of section .text:
+
+00000000 <kernaux_arch_i386_read_cr0>:
+   0:   0f 20 c0              mov    %cr0,%eax
+   3:   c3                    ret
+
+00000004 <kernaux_arch_i386_read_cr4>:
+   4:   0f 20 e0              mov    %cr4,%eax
+   7:   c3                    ret
+
+00000008 <kernaux_arch_i386_write_cr0>:
+   8:   8b 44 24 04           mov    0x4(%esp),%eax
+   c:   0f 22 c0              mov    %eax,%cr0
+   f:   c3                    ret
+
+00000010 <kernaux_arch_i386_write_cr3>:
+  10:   8b 44 24 04           mov    0x4(%esp),%eax
+  14:   0f 22 d8              mov    %eax,%cr3
+  17:   c3                    ret
+
+00000018 <kernaux_arch_i386_write_cr4>:
+  18:   8b 44 24 04           mov    0x4(%esp),%eax
+  1c:   0f 22 e0              mov    %eax,%cr4
+  1f:   c3                    ret
+```