Docs: add sync methods

Author: JPeer264

README.md

@@ -219,6 +219,8 @@ Let's exclude 4 classes and id's: `js`, `flexbox`, `canvas` and `svg`
 
 Store all matched selectors into the library and saves the new generated file with all renamed selectors.
 
+Sync: `processCssSync`
+
 Options:
 
 - overwrite (boolean): ensures that it does not overwrite the same file accidently. Default is `false`
@@ -248,6 +250,8 @@ rcs.processCss('**/*.css', options, err => {
 
 > **Important!** processCss should run first, otherwise there are no minified selectors
 
+Sync: `processJsSync`
+
 Options:
 
 - overwrite (boolean): ensures that it does not overwrite the same file accidently. Default is `false`
@@ -278,6 +282,8 @@ rcs.processJs('**/*.js', options, err => {
 
 Matches all strings `" "` or `' '` and replaces all matching words which are the same as the stored css values.
 
+Sync: `processSync`
+
 Options:
 
 - overwrite (boolean): ensures that it does not overwrite the same file accidently. Default is `false`