Cheatsheets added

- apk: Alpine Linux package manager
 - gcc: GNU C Compiler
 - grep: Pattern matcher in files or pipes
 - vim: Vi IMproved

cheatsheets/apk

@@ -0,0 +1,14 @@
+# Install a package
+apk add $package
+
+# Remove a package
+apk del $package
+
+# Update repos
+apk update
+
+# Upgrade all packages
+apk upgrade
+
+# Find a package
+apk search $package

cheatsheets/gcc

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+# Compile a file
+gcc file.c
+
+# Compile a file with a custom output
+gcc -o file file.c
+
+# Debug symbols
+gcc -g

cheatsheets/grep

@@ -0,0 +1,6 @@
+# Basic
+grep pattern file
+
+# Advanced
+grep -R pattern folder
+cat file | grep pattern

cheatsheets/vim

@@ -0,0 +1,8 @@
+# Appending
+a - drops vim into append mode
+i - enters append mode without character skip
+
+# File management
+:w - writes (saves) file
+:q - quits
+;q! - quits without saving changes