docs: use $HOME instead of ~ in Makefile examples

Amolith created 

Replace shell tilde expansion with explicit $HOME environment variable
in Makefile example commands for better clarity and consistency across
different shell environments.

Assisted-by: Kimi K2 Thinking via Crush <crush@charm.land>

Change summary

README.md | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

Detailed changes

README.md 🔗 

@@ -60,13 +60,13 @@ make list
 make all
 
 # Install specific skills to Claude Code
-SKILL_DIR=~/.claude/skills make authoring-skills formatting-commits
+SKILL_DIR=$HOME/.claude/skills make authoring-skills formatting-commits
 
 # Remove a specific skill from Amp
-make uninstall-authoring-skills SKILL_DIR=~/.config/agents/skills
+make uninstall-authoring-skills SKILL_DIR=$HOME/.config/agents/skills
 
 # Remove all skills from Codex
-make uninstall SKILL_DIR=~/.codex/skills
+make uninstall SKILL_DIR=$HOME/.codex/skills
 ```
 
 ### With symlinks